PL/SQL Pogramming Language - Quick Guide

The PL/SQL programming language was developed by Oracle Corporation in the late 1980s as procedural extension language for SQL and the Oracle relational database. Following are notable facts about PL/SQL:

• PL/SQL is a completely portable, high-performance transaction-processing language.
• PL/SQL provides a built-in interpreted and OS independent programming environment.
• PL/SQL can also directly be called from the command-line SQL*Plus interface.
• Direct call can also be made from external programming language calls to database.
• PL/SQL's general syntax is based on that of ADA and Pascal programming language.
• Apart from Oracle, PL/SQL is available in TimesTen in-memory database and IBM DB2.

PL/SQL - Environment Setup

PL/SQL is not a stand-alone programming language; it is a tool within the Oracle programming environment. SQL* Plus is an interactive tool that allows you to type SQL and PL/SQL statements at the command prompt. These commands are then sent to the database for processing. Once the statements are processed, the results are sent back and displayed on screen.
To run PL/SQL programs, you should have Oracle RBDMS Server installed in your machine which will take care of executing SQL commands. Most recent version of Oracle RDBMS is 11g. You can download a trial version of Oracle 11g from the following link:
Download Oracle 11g Express Edition
You will have to download either 32bit or 64 bit version of the installation as per your operating system. Usually there are two files, as I have downloaded for 64 bit Windows7. You will also use similar steps on your operating system, does not matter if it is Linux or Solaris.

• win64_11gR2_database_1of2.zip
• win64_11gR2_database_2of2.zip

After downloading above two files, you will need to unzip them in a single directory database and under that you will find following sub-directories:


 Finally, click on setup file to start the installation and follow the given steps till the end. If everything has been done successfully then its time to verify your installation. At your command prompt use the following command if you are using Windows:

sqlplus "/ as sysdba" 

If everything is fine, you should have SQL prompt where you will write your PL/SQL commands and scripts:

Text Editor

Running large programs from command prompt may land you in inadvertently losing some of the work. So a better option is to use command files. To use the command files:

• Type your code in a text editor, like Notepad, Notepad+, or EditPlus, etc.
• Save the file with the .sql extension in the home directory.
• Launch SQL*Plus command prompt from the directory where you created your PL/SQL file.
• Type @file_name at the SQL*Plus command prompt to execute your program.

If you are not using a file to execute PL/SQL scripts, then simply copy your PL/SQL code and then right click on the black window having SQL prompt and use paste option to paste complete code at the command prompt. Finally, just press enter to execute the code, if it is not already executed.

PL/SQL - Basic Syntax

PL/SQL is a block-structured language, meaning that PL/SQL programs are divided and written in logical blocks of code. Each block consists of three sub-parts:

S.N.	Sections & Description
1	Declarations This section starts with the keyword DECLARE. It is an optional section and defines all variables, cursors, subprograms, and other elements to be used in the program.
2	Executable Commands This section is enclosed between the keywords BEGIN and END and it is a mandatory section. It consists of the executable PL/SQL statements of the program. It should have at least one executable line of code, which may be just a NULL command to indicate that nothing should be executed.
3	Exception Handling This section starts with the keyword EXCEPTION. This section is again optional and contains exception(s) that handle errors in the program.

Every PL/SQL statement ends with a semicolon (;). PL/SQL blocks can be nested within other PL/SQL blocks using BEGIN and END. Here is the basic structure of a PL/SQL block:

DECLARE
   <declarations section>
BEGIN
   <executable command(s)>
EXCEPTION
   <exception handling>
END;

The 'Hello World' Example:

DECLARE
   message  varchar2(20):= 'Hello, World!';
BEGIN
   dbms_output.put_line(message);
END;
/

The end; line signals the end of the PL/SQL block. To run the code from SQL command line, you may need to type / at the beginning of the first blank line after the last line of the code. When the above code is executed at SQL prompt, it produces following result:

Hello World

PL/SQL procedure successfully completed.

PL/SQL - Data Types

PL/SQL variables, constants and parameters must have a valid data type which specifies a storage format, constraints, and valid range of values. This tutorial will take you through SCALAR and LOB data types available in PL/SQL and other two data types will be covered in other chapters.

Category	Description
Scalar	Single values with no internal components, such as a NUMBER, DATE, or BOOLEAN.
Large Object (LOB)	Pointers to large objects that are stored separately from other data items, such as text, graphic images, video clips, and sound waveforms.
Composite	Data items that have internal components that can be accessed individually. For example, collections and records.
Reference	Pointers to other data items.

PL/SQL Scalar Data Types and Subtypes

PL/SQL Scalar Data Types and Subtypes come under the following categories:

Date Type	Description
Numeric	Numeric values on which arithmetic operations are performed.
Character	Alphanumeric values that represent single characters or strings of characters.
Boolean	Logical values on which logical operations are performed.
Datetime	Dates and times.

PL/SQL provides subtypes of data types. For example, the data type NUMBER has a subtype called INTEGER. You can use subtypes in your PL/SQL program to make the data types compatible with data types in other programs while embedding PL/SQL code in another program, such as a Java program.

PL/SQL Numeric Data Types and Subtypes

Following is the detail of PL/SQL pre-defined numeric data types and their sub-types:

Data Type	Description
PLS_INTEGER	Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
BINARY_INTEGER	Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
BINARY_FLOAT	Single-precision IEEE 754-format floating-point number
BINARY_DOUBLE	Double-precision IEEE 754-format floating-point number
NUMBER(prec, scale)	Fixed-point or floating-point number with absolute value in range 1E-130 to (but not including) 1.0E126. A NUMBER variable can also represent 0.
DEC(prec, scale)	ANSI specific fixed-point type with maximum precision of 38 decimal digits.
DECIMAL(prec, scale)	IBM specific fixed-point type with maximum precision of 38 decimal digits.
NUMERIC(pre, secale)	Floating type with maximum precision of 38 decimal digits.
DOUBLE PRECISION	ANSI specific floating-point type with maximum precision of 126 binary digits (approximately 38 decimal digits)
FLOAT	ANSI and IBM specific floating-point type with maximum precision of 126 binary digits (approximately 38 decimal digits)
INT	ANSI specific integer type with maximum precision of 38 decimal digits
INTEGER	ANSI and IBM specific integer type with maximum precision of 38 decimal digits
SMALLINT	ANSI and IBM specific integer type with maximum precision of 38 decimal digits
REAL	Floating-point type with maximum precision of 63 binary digits (approximately 18 decimal digits)

Following is a valid declaration:

DECLARE
   num1 INTEGER;
   num2 REAL;
   num3 DOUBLE PRECISION;
BEGIN
   null;
END;
/

When the above code is compiled and executed, it produces the following result:

PL/SQL procedure successfully completed

PL/SQL Character Data Types and Subtypes

Following is the detail of PL/SQL pre-defined character data types and their sub-types:

Data Type	Description
CHAR	Fixed-length character string with maximum size of 32,767 bytes
VARCHAR2	Variable-length character string with maximum size of 32,767 bytes
RAW	Variable-length binary or byte string with maximum size of 32,767 bytes, not interpreted by PL/SQL
NCHAR	Fixed-length national character string with maximum size of 32,767 bytes
NVARCHAR2	Variable-length national character string with maximum size of 32,767 bytes
LONG	Variable-length character string with maximum size of 32,760 bytes
LONG RAW	Variable-length binary or byte string with maximum size of 32,760 bytes, not interpreted by PL/SQL
ROWID	Physical row identifier, the address of a row in an ordinary table
UROWID	Universal row identifier (physical, logical, or foreign row identifier)

PL/SQL Boolean Data Types

The BOOLEAN data type stores logical values that are used in logical operations. The logical values are the Boolean values TRUE and FALSE and the value NULL.
However, SQL has no data type equivalent to BOOLEAN. Therefore, Boolean values cannot be used in:

• SQL statements
• Built-in SQL functions (such as TO_CHAR)
• PL/SQL functions invoked from SQL statements

PL/SQL Datetime and Interval Types

The DATE datatype to store fixed-length datetimes, which include the time of day in seconds since midnight. Valid dates range from January 1, 4712 BC to December 31, 9999 AD.
The default date format is set by the Oracle initialization parameter NLS_DATE_FORMAT. For example, the default might be 'DD-MON-YY', which includes a two-digit number for the day of the month, an abbreviation of the month name, and the last two digits of the year, for example, 01-OCT-12.
Each DATE includes the century, year, month, day, hour, minute, and second. The following table shows the valid values for each field:

Field Name	Valid Datetime Values	Valid Interval Values
YEAR	-4712 to 9999 (excluding year 0)	Any nonzero integer
MONTH	01 to 12	0 to 11
DAY	01 to 31 (limited by the values of MONTH and YEAR, according to the rules of the calendar for the locale)	Any nonzero integer
HOUR	00 to 23	0 to 23
MINUTE	00 to 59	0 to 59
SECOND	00 to 59.9(n), where 9(n) is the precision of time fractional seconds	0 to 59.9(n), where 9(n) is the precision of interval fractional seconds
TIMEZONE_HOUR	-12 to 14 (range accommodates daylight savings time changes)	Not applicable
TIMEZONE_MINUTE	00 to 59	Not applicable
TIMEZONE_REGION	Found in the dynamic performance view V$TIMEZONE_NAMES	Not applicable
TIMEZONE_ABBR	Found in the dynamic performance view V$TIMEZONE_NAMES	Not applicable

PL/SQL Large Object (LOB) Data Types

Large object (LOB) data types refer large to data items such as text, graphic images, video clips, and sound waveforms. LOB data types allow efficient, random, piecewise access to this data. Following are the predefined PL/SQL LOB data types:

Data Type	Description	Size
BFILE	Used to store large binary objects in operating system files outside the database.	System-dependent. Cannot exceed 4 gigabytes (GB).
BLOB	Used to store large binary objects in the database.	8 to 128 terabytes (TB)
CLOB	Used to store large blocks of character data in the database.	8 to 128 TB
NCLOB	Used to store large blocks of NCHAR data in the database.	8 to 128 TB

PL/SQL User-Defined Subtypes

A subtype is a subset of another data type, which is called its base type. A subtype has the same valid operations as its base type, but only a subset of its valid values.
PL/SQL predefines several subtypes in package STANDARD. For example, PL/SQL predefines the subtypes CHARACTER and INTEGER as follows:

SUBTYPE CHARACTER IS CHAR;
SUBTYPE INTEGER IS NUMBER(38,0);

You can define and use your own subtypes. The following program illustrates defining and using a user-defined subtype:

DECLARE
   SUBTYPE name IS char(20);
   SUBTYPE message IS varchar2(100);
   salutation name;
   greetings message;
BEGIN
   salutation := 'Reader ';
   greetings := 'Welcome to the World of PL/SQL';
   dbms_output.put_line('Hello ' || salutation || greetings);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Hello Reader Welcome to the World of PL/SQL

PL/SQL procedure successfully completed.

NULLs in PL/SQL

PL/SQL NULL values represent missing or unknown data and they are not an integer, a character, or any other specific data type. Note that NULL is not the same as an empty data string or the null character value '\0'. A null can be assigned but it cannot be equated with anything, including itself.

PL/SQL - Variables

The name of a PL/SQL variable consists of a letter optionally followed by more letters, numerals, dollar signs, underscores, and number signs and should not exceed 30 characters. By default, variable names are not case-sensitive. You cannot use a reserved PL/SQL keyword as a variable name.

Variable Declaration in PL/SQL

PL/SQL variables must be declared in the declaration section or in a package as a global variable. When you declare a variable, PL/SQL allocates memory for the variable's value and the storage location is identified by the variable name.
The syntax for declaring a variable is:

variable_name [CONSTANT] datatype [NOT NULL] [:= | DEFAULT initial_value]

Where, variable_name is a valid identifier in PL/SQL, datatype must be a valid PL/SQL data type or any user defined data type which we already have discussed in last chapter. Some valid variable declarations along with their definition are shown below:

sales number(10, 2);
pi CONSTANT double precision := 3.1415;
name varchar2(25);
address varchar2(100);

When you provide a size, scale or precision limit with the data type, it is called a constrained declaration. Constrained declarations require less memory than unconstrained declarations. For example:

sales number(10, 2);
name varchar2(25);
address varchar2(100);

Initializing Variables in PL/SQL

Whenever you declare a variable, PL/SQL assigns it a default value of NULL. If you want to initialize a variable with a value other than the NULL value, you can do so during the declaration, using either of the following:

• The DEFAULT keyword
• The assignment operator

For example:

counter binary_integer := 0;
greetings varchar2(20) DEFAULT 'Have a Good Day';

You can also specify that a variable should not have a NULL value using the NOT NULL constraint. If you use the NOT NULL constraint, you must explicitly assign an initial value for that variable.
It is a good programming practice to initialize variables properly otherwise, sometime program would produce unexpected result. Try the following example which makes use of various types of variables:

DECLARE
   a integer := 10;
   b integer := 20;
   c integer;
   f real;
BEGIN
   c := a + b;
   dbms_output.put_line('Value of c: ' || c);
   f := 70.0/3.0;
   dbms_output.put_line('Value of f: ' || f);
END;
/

When the above code is executed, it produces the following result:

Value of c: 30
Value of f: 23.333333333333333333

PL/SQL procedure successfully completed.

Variable Scope in PL/SQL

PL/SQL allows the nesting of Blocks, i.e., each program block may contain another inner block. If a variable is declared within an inner block, it is not accessible to the outer block. However, if a variable is declared and accessible to an outer Block, it is also accessible to all nested inner Blocks. There are two types of variable scope:

• Local variables - variables declared in an inner block and not accessible to outer blocks.
• Global variables - variables declared in the outermost block or a package.

Following example shows the usage of Local and Global variables in its simple form:

DECLARE
   -- Global variables 
   num1 number := 95; 
   num2 number := 85; 
BEGIN 
   dbms_output.put_line('Outer Variable num1: ' || num1);
   dbms_output.put_line('Outer Variable num2: ' || num2);
   DECLARE 
      -- Local variables
      num1 number := 195; 
      num2 number := 185; 
   BEGIN 
      dbms_output.put_line('Inner Variable num1: ' || num1);
      dbms_output.put_line('Inner Variable num2: ' || num2);
   END; 
END;
/

When the above code is executed, it produces the following result:

Outer Variable num1: 95
Outer Variable num2: 85
Inner Variable num1: 195
Inner Variable num2: 185

PL/SQL procedure successfully completed.

PL/SQL - Constants and Literals

A constant holds a value that once declared, does not change in the program. A constant declaration specifies its name, data type, and value, and allocates storage for it. The declaration can also impose the NOT NULL constraint.

Declaring a Constant

A constant is declared using the CONSTANT keyword. It requires an initial value and does not allow that value to be changed. For example:

PI CONSTANT NUMBER := 3.141592654;

DECLARE
   -- constant declaration
   pi constant number := 3.141592654;
   -- other declarations
   radius number(5,2); 
   dia number(5,2); 
   circumference number(7, 2);
   area number (10, 2);
BEGIN 
   -- processing
   radius := 9.5; 
   dia := radius * 2; 
   circumference := 2.0 * pi * radius;
   area := pi * radius * radius;
   -- output
   dbms_output.put_line('Radius: ' || radius);
   dbms_output.put_line('Diameter: ' || dia);
   dbms_output.put_line('Circumference: ' || circumference);
   dbms_output.put_line('Area: ' || area);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Radius: 9.5
Diameter: 19
Circumference: 59.69
Area: 283.53

Pl/SQL procedure successfully completed.

The PL/SQL Literals

A literal is an explicit numeric, character, string, or Boolean value not represented by an identifier. For example, TRUE, 786, NULL, 'tutorialspoint' are all literals of type Boolean, number, or string. PL/SQL, literals are case-sensitive. PL/SQL supports the following kinds of literals:

• Numeric Literals
• Character Literals
• String Literals
• BOOLEAN Literals
• Date and Time Literals

The following table provides examples from all these categories of literal values.

Literal Type	Example:
Numeric Literals	050 78 -14 0 +32767 6.6667 0.0 -12.0 3.14159 +7800.00 6E5 1.0E-8 3.14159e0 -1E38 -9.5e-3
Character Literals	'A' '%' '9' ' ' 'z' '('
String Literals	'Hello, world!' 'Tutorials Point' '19-NOV-12'
BOOLEAN Literals	TRUE, FALSE, and NULL.
Date and Time Literals	DATE '1978-12-25'; TIMESTAMP '2012-10-29 12:01:01';

To embed single quotes within a string literal, place two single quotes next to each other as shown below:

DECLARE
   message  varchar2(20):= ''That''s tutorialspoint.com!'';
BEGIN
   dbms_output.put_line(message);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

That's tutorialspoint.com!

PL/SQL procedure successfully completed.

PL/SQL - Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulation. PL/SQL language is rich in built-in operators and provides the following type of operators:

• Arithmetic operators
• Relational operators
• Comparison operators
• Logical operators
• String operators

This tutorial will explain the arithmetic, relational, comparison and logical operators one by one. The String operators will be discussed under the chapter: PL/SQL - Strings.

Arithmetic Operators

Following table shows all the arithmetic operators supported by PL/SQL. Assume variable A holds 10 and variable B holds 5 then:

Operator	Description	Example
+	Adds two operands	A + B will give 15
-	Subtracts second operand from the first	A - B will give 5
*	Multiplies both operands	A * B will give 50
/	Divides numerator by de-numerator	A / B will give 2
**	Exponentiation operator, raises one operand to the power of other	A ** B will give 100000

Relational Operators

Relational operators compare two expressions or values and return a Boolean result. Following table shows all the relational operators supported by PL/SQL. Assume variable A holds 10 and variable B holds 20, then:

Operator	Description	Example
=	Checks if the values of two operands are equal or not, if yes then condition becomes true.	(A = B) is not true.
!= <> ~=	Checks if the values of two operands are equal or not, if values are not equal then condition becomes true.	(A != B) is true.
>	Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true.	(A > B) is not true.
<	Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true.	(A < B) is true.
>=	Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true.	(A >= B) is not true.
<=	Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true.	(A <= B) is true.

Comparison Operators

Comparison operators are used for comparing one expression to another. The result is always either TRUE, FALSE OR NULL.

Operator	Description	Example
LIKE	The LIKE operator compares a character, string, or CLOB value to a pattern and returns TRUE if the value matches the pattern and FALSE if it does not.	If 'Zara Ali' like 'Z% A_i' returns a Boolean true, whereas, 'Nuha Ali' like 'Z% A_i' returns a Boolean false.
BETWEEN	The BETWEEN operator tests whether a value lies in a specified range. x BETWEEN a AND b means that x >= a and x <= b.	If x = 10 then, x between 5 and 20 returns true, x between 5 and 10 returns true, but x between 11 and 20 returns false.
IN	The IN operator tests set membership. x IN (set) means that x is equal to any member of set.	If x = 'm' then, x in ('a', 'b', 'c') returns boolean false but x in ('m', 'n', 'o') returns Boolean true.
IS NULL	The IS NULL operator returns the BOOLEAN value TRUE if its operand is NULL or FALSE if it is not NULL. Comparisons involving NULL values always yield NULL.	If x = 'm', then 'x is null' returns Boolean false.

Logical Operators

Following table shows the Logical operators supported by PL/SQL. All these operators work on Boolean operands and produces Boolean results. Assume variable A holds true and variable B holds false, then:

Operator	Description	Example
and	Called logical AND operator. If both the operands are true then condition becomes true.	(A and B) is false.
or	Called logical OR Operator. If any of the two operands is true then condition becomes true.	(A or B) is true.
not	Called logical NOT Operator. Used to reverse the logical state of its operand. If a condition is true then Logical NOT operator will make it false.	not (A and B) is true.

PL/SQL Operator Precedence

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:
For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.
Here operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

Operator	Operation
**	exponentiation
+, -	identity, negation
*, /	multiplication, division
+, -, ||	addition, subtraction, concatenation
=, <, >, <=, >=, <>, !=, ~=, ^=, IS NULL, LIKE, BETWEEN, IN	comparison
NOT	logical negation
AND	conjunction
OR	inclusion

PL/SQL - Conditions

Decision-making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

IF-THEN Statement

It is the simplest form of IF control statement, frequently used in decision making and changing the control flow of the program execution.
The IF statement associates a condition with a sequence of statements enclosed by the keywords THEN and END IF. If the condition is TRUE, the statements get executed, and if the condition is FALSE or NULL, then the IF statement does nothing.

Syntax:

Syntax for IF-THEN statement is:

IF condition THEN 
   S;
END IF;

Where condition is a Boolean or relational condition and S is a simple or compound statement. Example of an IF-THEN statement is:

IF (a <= 20) THEN
   c:= c+1;
END IF;

If the Boolean expression condition evaluates to true, then the block of code inside the if statement will be executed. If Boolean expression evaluates to false, then the first set of code after the end of the if statement (after the closing end if) will be executed.

Flow Diagram:

IF-THEN-ELSE Statement

A sequence of IF-THEN statements can be followed by an optional sequence of ELSE statements, which execute when the condition is FALSE.

Syntax:

Syntax for the IF-THEN-ELSE statement is:

IF condition THEN
   S1; 
ELSE 
   S2;
END IF;

Where, S1 and S2 are different sequence of statements. In the IF-THEN-ELSE statements, when the test condition is TRUE, the statement S1 is executed and S2 is skipped; when the test condition is FALSE, then S1 is bypassed and statement S2 is executed. For example,

IF color = red THEN
  dbms_output.put_line('You have chosen a red car')
ELSE
  dbms_output.put_line('Please choose a color for your car');
END IF;

If the Boolean expression condition evaluates to true, then the if-then block of code will be executed, otherwise the else block of code will be executed.

Flow Diagram:

IF-THEN-ELSIF Statement

The IF-THEN-ELSIF statement allows you to choose between several alternatives. An IF-THEN statement can be followed by an optional ELSIF...ELSE statement. The ELSIF clause lets you add additional conditions.
When using IF-THEN-ELSIF statements there are few points to keep in mind.

• It's ELSIF, not ELSEIF
• An IF-THEN statement can have zero or one ELSE's and it must come after any ELSIF's.
• An IF-THEN statement can have zero to many ELSIF's and they must come before the ELSE.
• Once an ELSIF succeeds, none of the remaining ELSIF's or ELSE's will be tested.

Syntax:

The syntax of an IF-THEN-ELSIF Statement in PL/SQL programming language is:

IF(boolean_expression 1)THEN 
   S1; -- Executes when the boolean expression 1 is true 
ELSIF( boolean_expression 2) THEN
   S2;  -- Executes when the boolean expression 2 is true 
ELSIF( boolean_expression 3) THEN
   S3; -- Executes when the boolean expression 3 is true 
ELSE 
   S4; -- executes when the none of the above condition is true 
END IF;

CASE Statement

Like the IF statement, the CASE statement selects one sequence of statements to execute. However, to select the sequence, the CASE statement uses a selector rather than multiple Boolean expressions. A selector is an expression, whose value is used to select one of several alternatives.

Syntax:

The syntax for case statement in PL/SQL is:

CASE selector
    WHEN 'value1' THEN S1;
    WHEN 'value2' THEN S2;
    WHEN 'value3' THEN S3;
    ...
    ELSE Sn;  -- default case
END CASE;

Flow Diagram:

Searched CASE Statement

The searched CASE statement has no selector and its WHEN clauses contain search conditions that give Boolean values.

Syntax:

The syntax for searched case statement in PL/SQL is:

CASE
    WHEN selector = 'value1' THEN S1;
    WHEN selector = 'value2' THEN S2;
    WHEN selector = 'value3' THEN S3;
    ...
    ELSE Sn;  -- default case
END CASE;

Flow Diagram:

Nested IF-THEN-ELSE Statements

It is always legal in PL/SQL programming to nest IF-ELSE statements, which means you can use one IF or ELSE IF statement inside another IF or ELSE IF statement(s).

Syntax:

IF( boolean_expression 1)THEN
    -- executes when the boolean expression 1 is true 
    IF(boolean_expression 2) THEN
      -- executes when the boolean expression 2 is true 
      sequence-of-statements;
   END IF;
ELSE
   -- executes when the boolean expression 1 is not true
  else-statements;
END IF;

PL/SQL - Loops

There may be a situation when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.
Programming languages provide various control structures that allow for more complicated execution paths.
A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages:

Basic Loop Statement

Basic loop structure encloses sequence of statements in between the LOOP and END LOOP statements. With each iteration, the sequence of statements is executed and then control resumes at the top of the loop.

Syntax:

The syntax of a basic loop in PL/SQL programming language is:

LOOP
  Sequence of statements;
END LOOP;

Here, sequence of statement(s) may be a single statement or a block of statements. An EXIT statement or an EXIT WHEN statement is required to break the loop.

WHILE LOOP Statement

A WHILE LOOP statement in PL/SQL programming language repeatedly executes a target statement as long as a given condition is true.

Syntax:

WHILE condition LOOP
   sequence_of_statements
END LOOP;

FOR LOOP Statement

A FOR LOOP is a repetition control structure that allows you to efficiently write a loop that needs to execute a specific number of times.

Syntax:

FOR counter IN initial_value .. final_value LOOP
   sequence_of_statements;
END LOOP;

Following are some special characteristics of PL/SQL for loop:

• The initial_value and final_value of the loop variable or counter can be literals, variables, or expressions but must evaluate to numbers. Otherwise, PL/SQL raises the predefined exception VALUE_ERROR.
• The initial_value need not to be 1; however, the loop counter increment (or decrement) must be 1.
• PL/SQL allows determine the loop range dynamically at run time.

Nested Loops

PL/SQL allows using one loop inside another loop. Following section shows few examples to illustrate the concept.
The syntax for a nested basic LOOP statement in PL/SQL is as follows:

LOOP
   Sequence of statements1
   LOOP
      Sequence of statements2
   END LOOP;
END LOOP;

The syntax for a nested FOR LOOP statement in PL/SQL is as follows:

FOR counter1 IN initial_value1 .. final_value1 LOOP
   sequence_of_statements1
   FOR counter2 IN initial_value2 .. final_value2 LOOP
      sequence_of_statements2
   END LOOP;
END LOOP;

The syntax for a nested WHILE LOOP statement in Pascal is as follows:

WHILE condition1 LOOP
   sequence_of_statements1
   WHILE condition2 LOOP
      sequence_of_statements2
   END LOOP;
END LOOP;

EXIT Statement

The EXIT statement in PL/SQL programming language has following two usages:

• When the EXIT statement is encountered inside a loop, the loop is immediately terminated and program control resumes at the next statement following the loop.
• If you are using nested loops (i.e. one loop inside another loop), the EXIT statement will stop the execution of the innermost loop and start executing the next line of code after the block.

Syntax:

The syntax for a EXIT statement in PL/SQL is as follows:

EXIT;

Flow Diagram:

CONTINUE Statement

The CONTINUE statement causes the loop to skip the remainder of its body and immediately retest its condition prior to reiterating. In other words, it forces the next iteration of the loop to take place, skipping any code in between.

Syntax:

The syntax for a CONTINUE statement is as follows:

CONTINUE;

Flow Diagram:

GOTO Statement

A GOTO statement in PL/SQL programming language provides an unconditional jump from the GOTO to a labeled statement in the same subprogram.
NOTE: Use of GOTO statement is highly discouraged in any programming language because it makes difficult to trace the control flow of a program, making the program hard to understand and hard to modify. Any program that uses a GOTO can be rewritten so that it doesn't need the GOTO.

Syntax:

The syntax for a GOTO statement in PL/SQL is as follows:

GOTO label;
..
..
<< label >>
statement;

Flow Diagram:

PL/SQL - Strings

The string in PL/SQL is actually a sequence of characters with an optional size specification. The characters could be numeric, letters, blank, special characters or a combination of all. PL/SQL offers three kinds of strings:

• Fixed-length strings: In such strings, programmers specify the length while declaring the string. The string is right-padded with spaces to the length so specified.
• Variable-length strings: In such strings, a maximum length up to 32,767, for the string is specified and no padding takes place.
• Character large objects (CLOBs): These are variable-length strings that can be up to 128 terabytes.

PL/SQL strings could be either variables or literals. A string literal is enclosed within quotation marks. For example,

'This is a string literal.' Or 'hello world'

To include a single quote inside a string literal, you need to type two single quotes next to one another, like:

'this isn''t what it looks like'

Declaring String Variables

Oracle database provides numerous string datatypes , like, CHAR, NCHAR, VARCHAR2, NVARCHAR2, CLOB, and NCLOB. The datatypes prefixed with an 'N' are 'national character set' datatypes, that store Unicode character data.
If you need to declare a variable-length string, you must provide the maximum length of that string. For example, the VARCHAR2 data type. The following example illustrates declaring and using some string variables:

DECLARE
   name varchar2(20);
   company varchar2(30);
   introduction clob;
   choice char(1);
BEGIN
   name := 'John Smith';
   company := 'Infotech';
   introduction := ' Hello! I''m John Smith from Infotech.';
   choice := 'y';
   IF choice = 'y' THEN
      dbms_output.put_line(name);
      dbms_output.put_line(company);
      dbms_output.put_line(introduction);
   END IF;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

John Smith
Infotech Corporation
Hello! I'm John Smith from Infotech.

PL/SQL procedure successfully completed

To declare a fixed-length string, use the CHAR datatype. Here you do not have to specify a maximum length for a fixed-length variable. If you leave off the length constraint, Oracle Database automatically uses a maximum length required. So following two declarations below are identical:

 red_flag CHAR(1) := 'Y';
 red_flag CHAR    := 'Y';

PL/SQL - Arrays

PL/SQL programming language provides a data structure called the VARRAY, which can store a fixed-size sequential collection of elements of the same type. A varray is used to store an ordered collection of data, but it is often more useful to think of an array as a collection of variables of the same type.
All varrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.



An array is a part of collection type data and it stands for variable-size arrays. We will study other collection types in a later chapter 'PL/SQL Collections'.
Each element in a varray has an index associated with it. It also has a maximum size that can be changed dynamically.

Creating a Varray Type

A varray type is created with the CREATE TYPE statement. You must specify the maximum size and the type of elements stored in the varray.
The basic syntax for creating a VRRAY type at the schema level is:

CREATE OR REPLACE TYPE varray_type_name IS VARRAY(n) of <element_type>

Where,

• varray_type_name is a valid attribute name,
• n is the number of elements (maximum) in the varray,
• element_type is the data type of the elements of the array.

Maximum size of a varray can be changed using the ALTER TYPE statement.
For example,

CREATE Or REPLACE TYPE namearray AS VARRAY(3) OF VARCHAR2(10);
/

Type created.

The basic syntax for creating a VRRAY type within a PL/SQL block is:

TYPE varray_type_name IS VARRAY(n) of <element_type>

For example:

TYPE namearray IS VARRAY(5) OF VARCHAR2(10);
Type grades IS VARRAY(5) OF INTEGER;

PL/SQL - Procedures

A subprogram is a program unit/module that performs a particular task. These subprograms are combined to form larger programs. This is basically called the 'Modular design'. A subprogram can be invoked by another subprogram or program which is called the calling program.
A subprogram can be created:

• At schema level
• Inside a package
• Inside a PL/SQL block

A schema level subprogram is a standalone subprogram. It is created with the CREATE PROCEDURE or CREATE FUNCTION statement. It is stored in the database and can be deleted with the DROP PROCEDURE or DROP FUNCTION statement.
A subprogram created inside a package is a packaged subprogram. It is stored in the database and can be deleted only when the package is deleted with the DROP PACKAGE statement. We will discuss packages in the chapter 'PL/SQL - Packages'.
PL/SQL subprograms are named PL/SQL blocks that can be invoked with a set of parameters. PL/SQL provides two kinds of subprograms:

• Functions: these subprograms return a single value, mainly used to compute and return a value.
• Procedures: these subprograms do not return a value directly, mainly used to perform an action.

This chapter is going to cover important aspects of a PL/SQL procedure and we will cover PL/SQL function in next chapter.

Parts of a PL/SQL Subprogram

Each PL/SQL subprogram has a name, and may have a parameter list. Like anonymous PL/SQL blocks and, the named blocks a subprograms will also have following three parts:

S.N.	Parts & Description
1	Declarative Part It is an optional part. However, the declarative part for a subprogram does not start with the DECLARE keyword. It contains declarations of types, cursors, constants, variables, exceptions, and nested subprograms. These items are local to the subprogram and cease to exist when the subprogram completes execution.
2	Executable Part This is a mandatory part and contains statements that perform the designated action.
3	Exception-handling This is again an optional part. It contains the code that handles run-time errors.

Creating a Procedure

A procedure is created with the CREATE OR REPLACE PROCEDURE statement. The simplified syntax for the CREATE OR REPLACE PROCEDURE statement is as follows:

CREATE [OR REPLACE] PROCEDURE procedure_name
[(parameter_name [IN | OUT | IN OUT] type [, ...])]
{IS | AS}
BEGIN
  < procedure_body >
END procedure_name;

Where,

• procedure-name specifies the name of the procedure.
• [OR REPLACE] option allows modifying an existing procedure.
• The optional parameter list contains name, mode and types of the parameters. IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure.
• procedure-body contains the executable part.
• The AS keyword is used instead of the IS keyword for creating a standalone procedure.

PL/SQL - Functions

A PL/SQL function is same as a procedure except that it returns a value.

Creating a Function

A standalone function is created using the CREATE FUNCTION statement. The simplified syntax for the CREATE OR REPLACE PROCEDURE statement is as follows:

CREATE [OR REPLACE] FUNCTION function_name
[(parameter_name [IN | OUT | IN OUT] type [, ...])]
RETURN return_datatype
{IS | AS}
BEGIN
   < function_body >
END [function_name];

Where,

• function-name specifies the name of the function.
• [OR REPLACE] option allows modifying an existing function.
• The optional parameter list contains name, mode and types of the parameters. IN represents that value will be passed from outside and OUT represents that this parameter will be used to return a value outside of the procedure.
• RETURN clause specifies that data type you are going to return from the function.
• function-body contains the executable part.
• function-body must contain a RETURN statement.
• The AS keyword is used instead of the IS keyword for creating a standalone function.

PL/SQL - Cursors

Oracle creates a memory area, known as context area, for processing an SQL statement, which contains all information needed for processing the statement, for example, number of rows processed, etc.
A cursor is a pointer to this context area. PL/SQL controls the context area through a cursor. A cursor holds the rows (one or more) returned by a SQL statement. The set of rows the cursor holds is referred to as the active set.
You can name a cursor so that it could be referred to in a program to fetch and process the rows returned by the SQL statement, one at a time. There are two types of cursors:

• Implicit cursors
• Explicit cursors

Implicit Cursors

Implicit cursors are automatically created by Oracle whenever an SQL statement is executed, when there is no explicit cursor for the statement. Programmers cannot control the implicit cursors and the information in it.
Whenever a DML statement (INSERT, UPDATE and DELETE) is issued, an implicit cursor is associated with this statement. For INSERT operations, the cursor holds the data that needs to be inserted. For UPDATE and DELETE operations, the cursor identifies the rows that would be affected.
In PL/SQL, you can refer to the most recent implicit cursor as the SQL cursor, which always has the attributes like %FOUND, %ISOPEN, %NOTFOUND, and %ROWCOUNT. The SQL cursor has additional attributes, %BULK_ROWCOUNT and %BULK_EXCEPTIONS, designed for use with the FORALL statement.

Explicit Cursors

Explicit cursors are programmer defined cursors for gaining more control over the context area. An explicit cursor should be defined in the declaration section of the PL/SQL Block. It is created on a SELECT Statement which returns more than one row.
The syntax for creating an explicit cursor is :

CURSOR cursor_name IS select_statement;

Working with an explicit cursor involves four steps:

• Declaring the cursor for initializing in the memory
• Opening the cursor for allocating memory
• Fetching the cursor for retrieving data
• Closing the cursor to release allocated memory

Declaring the Cursor

Declaring the cursor defines the cursor with a name and the associated SELECT statement. For example:

CURSOR c_customers IS
   SELECT id, name, address FROM customers;

Opening the Cursor

Opening the cursor allocates memory for the cursor and makes it ready for fetching the rows returned by the SQL statement into it. For example, we will open above-defined cursor as follows:

OPEN c_customers;

Fetching the Cursor

Fetching the cursor involves accessing one row at a time. For example we will fetch rows from the above-opened cursor as follows:

FETCH c_customers INTO c_id, c_name, c_addr;

Closing the Cursor

Closing the cursor means releasing the allocated memory. For example, we will close above-opened cursor as follows:

CLOSE c_customers;

Example:

Following is a complete example to illustrate the concepts of explicit cursors:

DECLARE
   c_id customers.id%type;
   c_name customers.name%type;
   c_addr customers.address%type;
   CURSOR c_customers is
      SELECT id, name, address FROM customers;
BEGIN
   OPEN c_customers;
   LOOP
      FETCH c_customers into c_id, c_name, c_addr;
      dbms_output.put_line(c_id || ' ' || c_name || ' ' || c_addr);
      EXIT WHEN c_customers%notfound;
   END LOOP;
   CLOSE c_customers;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

1 Ramesh Ahmedabad 
2 Khilan Delhi 
3 kaushik Kota    
4 Chaitali Mumbai 
5 Hardik Bhopal  
6 Komal MP  

PL/SQL procedure successfully completed.

PL/SQL - Records

A PL/SQL record is a data structure that can hold data items of different kinds. Records consist of different fields, similar to a row of a database table.
PL/SQL can handle the following types of records:

• Table-based
• Cursor-based records
• User-defined records

Table-Based Records

The %ROWTYPE attribute enables a programmer to create table-based and cursor-based records.
The following example would illustrate the concept of table-based records. We will be using the CUSTOMERS table we had created and used in the previous chapters:

DECLARE
   customer_rec customers%rowtype;
BEGIN
   SELECT * into customer_rec
   FROM customers
   WHERE id = 5;

   dbms_output.put_line('Customer ID: ' || customer_rec.id);
   dbms_output.put_line('Customer Name: ' || customer_rec.name);
   dbms_output.put_line('Customer Address: ' || customer_rec.address);
   dbms_output.put_line('Customer Salary: ' || customer_rec.salary);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Customer ID: 5
Customer Name: Hardik
Customer Address: Bhopal
Customer Salary: 9000

PL/SQL procedure successfully completed.

Cursor-Based Records

The following example would illustrate the concept of cursor-based records. We will be using the CUSTOMERS table we had created and used in the previous chapters:

DECLARE
   CURSOR customer_cur is
      SELECT id, name, address 
      FROM customers;
   customer_rec customer_cur%rowtype;
BEGIN
   OPEN customer_cur;
   LOOP
      FETCH customer_cur into customer_rec;
      EXIT WHEN customer_cur%notfound;
      DBMS_OUTPUT.put_line(customer_rec.id || ' ' || customer_rec.name);
   END LOOP;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

1 Ramesh
2 Khilan
3 kaushik
4 Chaitali
5 Hardik
6 Komal

PL/SQL procedure successfully completed.

User-Defined Records

PL/SQL provides a user-defined record type that allows you to define different record structures. Records consist of different fields. Suppose you want to keep track of your books in a library. You might want to track the following attributes about each book:

• Title
• Author
• Subject
• Book ID

Defining a Record

The record type is defined as:

TYPE
type_name IS RECORD
  ( field_name1  datatype1  [NOT NULL]  [:= DEFAULT EXPRESSION],
   field_name2   datatype2   [NOT NULL]  [:= DEFAULT EXPRESSION],
   ...
   field_nameN  datatypeN  [NOT NULL]  [:= DEFAULT EXPRESSION);
record-name  type_name;

Here is the way you would declare the Book record:

DECLARE
TYPE books IS RECORD
(title  varchar(50),
    author  varchar(50),
    subject varchar(100),
    book_id   number);
book1 books;
book2 books;

Accessing Fields

To access any field of a record, we use the dot (.) operator. The member access operator is coded as a period between the record variable name and the field that we wish to access. Following is the example to explain usage of record:

DECLARE
   type books is record
      (title varchar(50),
       author varchar(50),
       subject varchar(100),
       book_id number);
   book1 books;
   book2 books;
BEGIN
   -- Book 1 specification
   book1.title  := 'C Programming';
   book1.author := 'Nuha Ali '; 
   book1.subject := 'C Programming Tutorial';
   book1.book_id := 6495407;

   -- Book 2 specification
   book2.title := 'Telecom Billing';
   book2.author := 'Zara Ali';
   book2.subject := 'Telecom Billing Tutorial';
   book2.book_id := 6495700;

   -- Print book 1 record
   dbms_output.put_line('Book 1 title : '|| book1.title);
   dbms_output.put_line('Book 1 author : '|| book1.author);
   dbms_output.put_line('Book 1 subject : '|| book1.subject);
   dbms_output.put_line('Book 1 book_id : ' || book1.book_id);
  
   -- Print book 2 record
   dbms_output.put_line('Book 2 title : '|| book2.title);
   dbms_output.put_line('Book 2 author : '|| book2.author);
   dbms_output.put_line('Book 2 subject : '|| book2.subject);
   dbms_output.put_line('Book 2 book_id : '|| book2.book_id);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700

PL/SQL procedure successfully completed.

PL/SQL - Exceptions

An error condition during a program execution is called an exception in PL/SQL. PL/SQL supports programmers to catch such conditions using EXCEPTION block in the program and an appropriate action is taken against the error condition. There are two types of exceptions:

• System-defined exceptions
• User-defined exceptions

Syntax for Exception Handling

The General Syntax for exception handling is as follows. Here, you can list down as many as exceptions you want to handle. The default exception will be handled using WHEN others THEN:

DECLARE
   <declarations section>
BEGIN
   <executable command(s)>
EXCEPTION
   <exception handling goes here >
   WHEN exception1 THEN 
       exception1-handling-statements 
   WHEN exception2  THEN 
      exception2-handling-statements 
   WHEN exception3 THEN 
      exception3-handling-statements
   ........
   WHEN others THEN
      exception3-handling-statements
END;

Example

Let us write some simple code to illustrate the concept. We will be using the CUSTOMERS table we had created and used in the previous chapters:

DECLARE
   c_id customers.id%type := 8;
   c_name  customers.name%type;
   c_addr customers.address%type;
BEGIN
   SELECT  name, address INTO  c_name, c_addr
   FROM customers
   WHERE id = c_id;

   DBMS_OUTPUT.PUT_LINE ('Name: '||  c_name);
   DBMS_OUTPUT.PUT_LINE ('Address: ' || c_addr);
EXCEPTION
   WHEN no_data_found THEN
      dbms_output.put_line('No such customer!');
   WHEN others THEN
      dbms_output.put_line('Error!');
END;
/

When the above code is executed at SQL prompt, it produces the following result:

No such customer!

PL/SQL procedure successfully completed.

The above program displays the name and address of a customer whose ID is given. Since there is no customer with ID value 8 in our database, the program raises the run-time exception NO_DATA_FOUND which is captured in EXCEPTION block.

PL/SQL - Triggers

Triggers are stored programs, which are automatically executed or fired when some events occur. Triggers are, in fact, written to be executed in response to any of the following events:

• A database manipulation (DML) statement (DELETE, INSERT, or UPDATE).
• A database definition (DDL) statement (CREATE, ALTER, or DROP).
• A database operation (SERVERERROR, LOGON, LOGOFF, STARTUP, or SHUTDOWN).

Triggers could be defined on the table, view, schema, or database with which the event is associated.

Creating Triggers

The syntax for creating a trigger is:

CREATE [OR REPLACE ] TRIGGER trigger_name 
{BEFORE | AFTER | INSTEAD OF } 
{INSERT [OR] | UPDATE [OR] | DELETE} 
[OF col_name] 
ON table_name 
[REFERENCING OLD AS o NEW AS n] 
[FOR EACH ROW] 
WHEN (condition)  
DECLARE
   Declaration-statements
BEGIN 
   Executable-statements
EXCEPTION
   Exception-handling-statements
END;

Where,

• CREATE [OR REPLACE] TRIGGER trigger_name : Creates or replaces an existing trigger with the trigger_name.
• {BEFORE | AFTER | INSTEAD OF}: This specifies when the trigger would be executed. The INSTEAD OF clause is used for creating trigger on a view.
• {INSERT [OR] | UPDATE [OR] | DELETE}: This specifies the DML operation.
• [OF col_name]: This specifies the column name that would be updated.
• [ON table_name]: This specifies the name of the table associated with the trigger.
• [REFERENCING OLD AS o NEW AS n]: This allows you to refer new and old values for various DML statements, like INSERT, UPDATE, and DELETE.
• [FOR EACH ROW]: This specifies a row level trigger, i.e., the trigger would be executed for each row being affected. Otherwise the trigger will execute just once when the SQL statement is executed, which is called a table level trigger.
• WHEN (condition): This provides a condition for rows for which the trigger would fire. This clause is valid only for row level triggers.

Example:

To start with, we will be using the CUSTOMERS table:

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME     | AGE | ADDRESS   | SALARY   |
+----+----------+-----+-----------+----------+
|  1 | Ramesh   |  32 | Ahmedabad |  2000.00 |
|  2 | Khilan   |  25 | Delhi     |  1500.00 |
|  3 | kaushik  |  23 | Kota      |  2000.00 |
|  4 | Chaitali |  25 | Mumbai    |  6500.00 |
|  5 | Hardik   |  27 | Bhopal    |  8500.00 |
|  6 | Komal    |  22 | MP        |  4500.00 |
+----+----------+-----+-----------+----------+

The following program creates a row level trigger for the customers table that would fire for INSERT or UPDATE or DELETE operations performed on the CUSTOMERS table. This trigger will display the salary difference between the old values and new values:

CREATE OR REPLACE TRIGGER display_salary_changes
BEFORE DELETE OR INSERT OR UPDATE ON customers
FOR EACH ROW
WHEN (NEW.ID > 0)
DECLARE
   sal_diff number;
BEGIN
   sal_diff := :NEW.salary  - :OLD.salary;
   dbms_output.put_line('Old salary: ' || :OLD.salary);
   dbms_output.put_line('New salary: ' || :NEW.salary);
   dbms_output.put_line('Salary difference: ' || sal_diff);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Trigger created.

Here following two points are important and should be noted carefully:

• OLD and NEW references are not available for table level triggers, rather you can use them for record level triggers.
• If you want to query the table in the same trigger, then you should use the AFTER keyword, because triggers can query the table or change it again only after the initial changes are applied and the table is back in a consistent state.
• Above trigger has been written in such a way that it will fire before any DELETE or INSERT or UPDATE operation on the table, but you can write your trigger on a single or multiple operations, for example BEFORE DELETE, which will fire whenever a record will be deleted using DELETE operation on the table.

PL/SQL - Packages

PL/SQL packages are schema objects that groups logically related PL/SQL types, variables and subprograms.
A package will have two mandatory parts:

• Package specification
• Package body or definition

Package Specification

The specification is the interface to the package. It just DECLARES the types, variables, constants, exceptions, cursors, and subprograms that can be referenced from outside the package. In other words, it contains all information about the content of the package, but excludes the code for the subprograms.
All objects placed in the specification are called public objects. Any subprogram not in the package specification but coded in the package body is called a private object.
The following code snippet shows a package specification having a single procedure. You can have many global variables defined and multiple procedures or functions inside a package.

CREATE PACKAGE cust_sal AS
   PROCEDURE find_sal(c_id customers.id%type);
END cust_sal;
/

When the above code is executed at SQL prompt, it produces the following result:

Package created.

Package Body

The package body has the codes for various methods declared in the package specification and other private declarations, which are hidden from code outside the package.
The CREATE PACKAGE BODY Statement is used for creating the package body. The following code snippet shows the package body declaration for the cust_sal package created above. I assumed that we already have CUSTOMERS table created in our database as mentioned in PL/SQL - Variables chapter.

CREATE OR REPLACE PACKAGE BODY cust_sal AS
   PROCEDURE find_sal(c_id customers.id%TYPE) IS
   c_sal customers.salary%TYPE;
   BEGIN
      SELECT salary INTO c_sal
      FROM customers
      WHERE id = c_id;
      dbms_output.put_line('Salary: '|| c_sal);
   END find_sal;
END cust_sal;
/

When the above code is executed at SQL prompt, it produces the following result:

Package body created.

Using the Package Elements

The package elements (variables, procedures or functions) are accessed with the following syntax:

package_name.element_name;

Consider, we already have created above package in our database schema, the following program uses the find_sal method of the cust_sal package:

DECLARE
   code customers.id%type := &cc_id;
BEGIN
   cust_sal.find_sal(code);
END;
/

When the above code is executed at SQL prompt, it prompt to enter customer ID, and when you enter an ID, it displays the corresponding salary as follows:

Enter value for cc_id: 1
Salary: 3000

PL/SQL procedure successfully completed.

PL/SQL - Collections

A collection is an ordered group of elements having the same data type. Each element is identified by a unique subscript that represents its position in the collection.
PL/SQL provides three collection types:

• Index-by tables or Associative array
• Nested table
• Variable-size array or Varray

Index-By Table

An index-by table (also called an associative array) is a set of key-value pairs. Each key is unique, and is used to locate the corresponding value. The key can be either an integer or a string.
An index-by table is created using the following syntax. Here we are creating an index-by table named table_name whose keys will be of subscript_type and associated values will be of element_type

TYPE type_name IS TABLE OF element_type [NOT NULL] INDEX BY subscript_type;

table_name type_name;

Example:

Following example how to create a table to store integer values along with names and later it prints the same list of names.

DECLARE
   TYPE salary IS TABLE OF NUMBER INDEX BY VARCHAR2(20);
   salary_list salary;
   name   VARCHAR2(20);
BEGIN
   -- adding elements to the table
   salary_list('Rajnish')  := 62000;
   salary_list('Minakshi')  := 75000;
   salary_list('Martin') := 100000;
   salary_list('James') := 78000;

   -- printing the table
   name := salary_list.FIRST;
   WHILE name IS NOT null LOOP
      dbms_output.put_line
      ('Salary of ' || name || ' is ' || TO_CHAR(salary_list(name)));
      name := salary_list.NEXT(name);
   END LOOP;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Salary of Rajnish is 62000
Salary of Minakshi is 75000
Salary of Martin is 100000
Salary of James is 78000

PL/SQL procedure successfully completed.

Nested Tables

A nested table is like a one-dimensional array with an arbitrary number of elements. However, a nested table differs from an array in the following aspects:

• An array has a declared number of elements, but a nested table does not. The size of a nested table can increase dynamically.
• An array is always dense i.e., it always has consecutive subscripts. A nested array is dense initially, but it can become sparse when elements are deleted from it.

An nested table is created using the following syntax:

TYPE type_name IS TABLE OF element_type [NOT NULL];

table_name type_name;

This declaration is similar to declaration of an index-by table, but there is no INDEX BY clause.
A nested table can be stored in a database column and so it could be used for simplifying SQL operations where you join a single-column table with a larger table. An associative array cannot be stored in the database.

Example:

The following examples illustrate the use of nested table:

DECLARE
   TYPE names_table IS TABLE OF VARCHAR2(10);
   TYPE grades IS TABLE OF INTEGER;

   names names_table;
   marks grades;
   total integer;
BEGIN
   names := names_table('Kavita', 'Pritam', 'Ayan', 'Rishav', 'Aziz');
   marks:= grades(98, 97, 78, 87, 92);
   total := names.count;
   dbms_output.put_line('Total '|| total || ' Students');
   FOR i IN 1 .. total LOOP
      dbms_output.put_line('Student:'||names(i)||', Marks:' || marks(i));
   end loop;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Total 5 Students
Student:Kavita, Marks:98
Student:Pritam, Marks:97
Student:Ayan, Marks:78
Student:Rishav, Marks:87
Student:Aziz, Marks:92

PL/SQL procedure successfully completed.

PL/SQL - Transactions

A database transaction is an atomic unit of work that may consist of one or more related SQL statements. It is called atomic because the database modifications brought about by the SQL statements that constitute a transaction can collectively be either committed, i.e., made permanent to the database or rolled back (undone) from the database.
A successfully executed SQL statement and a committed transaction are not same. Even if an SQL statement is executed successfully, unless the transaction containing the statement is committed, it can be rolled back and all changes made by the statement(s) can be undone.

Starting an Ending a Transaction

A transaction has a beginning and an end. A transaction starts when one of the following events take place:

• The first SQL statement is performed after connecting to the database.
• At each new SQL statement issued after a transaction is completed.

A transaction ends when one of the following events take place:

• A COMMIT or a ROLLBACK statement is issued.
• A DDL statement, like CREATE TABLE statement, is issued; because in that case a COMMIT is automatically performed.
• A DCL statement, such as a GRANT statement, is issued; because in that case a COMMIT is automatically performed.
• User disconnects from the database.
• User exits from SQL*PLUS by issuing the EXIT command, a COMMIT is automatically performed.
• SQL*Plus terminates abnormally, a ROLLBACK is automatically performed.
• A DML statement fails; in that case a ROLLBACK is automatically performed for undoing that DML statement.

Committing a Transaction

A transaction is made permanent by issuing the SQL command COMMIT. The general syntax for the COMMIT command is:

COMMIT;

Rolling Back Transactions

Changes made to the database without COMMIT could be undone using the ROLLBACK command.
The general syntax for the ROLLBACK command is:

ROLLBACK [TO SAVEPOINT < savepoint_name>];

When a transaction is aborted due to some unprecedented situation, like system failure, the entire transaction since a commit is automatically rolled back. If you are not using savepoiny, then simply use the following statement to rollback all the changes:

ROLLBACK;

Savepoints

Savepoints are sort of markers that help in splitting a long transaction into smaller units by setting some checkpoints. By setting savepoints within a long transaction, you can roll back to a checkpoint if required. This is done by issuing the SAVEPOINT command.
The general syntax for the SAVEPOINT command is:

SAVEPOINT < savepoint_name >;

Automatic Transaction Control

To execute a COMMIT automatically whenever an INSERT, UPDATE or DELETE command is executed, you can set the AUTOCOMMIT environment variable as:

SET AUTOCOMMIT ON;

You can turn-off auto commit mode using the following command:

SET AUTOCOMMIT OFF;

PL/SQL - Date & Time

PL/SQL provides two classes of date and time related data types:

• Datetime data types
• Interval data types

The Datetime data types are:

• DATE
• TIMESTAMP
• TIMESTAMP WITH TIME ZONE
• TIMESTAMP WITH LOCAL TIME ZONE

The Interval data types are:

• INTERVAL YEAR TO MONTH
• INTERVAL DAY TO SECOND

The Datetime Data Types

Following are the Datetime data types:

• DATE - it stores date and time information in both character and number datatypes. It is made of information on century, year, month, date, hour, minute, and second. It is specified as:
• TIMESTAMP - it is an extension of the DATE datatype. It stores the year, month, and day of the DATE datatype, along with hour, minute, and second values. It is useful for storing precise time values.
• TIMESTAMP WITH TIME ZONE - it is a variant of TIMESTAMP that includes a time zone region name or a time zone offset in its value. The time zone offset is the difference (in hours and minutes) between local time and UTC. This datatype is useful for collecting and evaluating date information across geographic regions.
• TIMESTAMP WITH LOCAL TIME ZONE - it is another variant of TIMESTAMP that includes a time zone offset in its value.

Examples:

SELECT SYSDATE FROM DUAL;

Output:

08/31/2012 5:25:34 PM

SELECT TO_CHAR(CURRENT_DATE, 'DD-MM-YYYY HH:MI:SS') FROM DUAL;

Output:

31-08-2012 05:26:14

SELECT ADD_MONTHS(SYSDATE, 5) FROM DUAL;

Output:

01/31/2013 5:26:31 PM

SELECT LOCALTIMESTAMP FROM DUAL;

Output:

8/31/2012 5:26:55.347000 PM

The Interval Data Types

Following are the Interval data types:

• INTERVAL YEAR TO MONTH - it stores a period of time using the YEAR and MONTH datetime fields.
• INTERVAL DAY TO SECOND - it stores a period of time in terms of days, hours, minutes, and seconds.

PL/SQL - DBMS Output

The DBMS_OUTPUT is a built-in package that enables you to display output, display debugging information, and send messages from PL/SQL blocks, subprograms, packages, and triggers.

Example:

DECLARE
   lines dbms_output.chararr;
   num_lines number;
BEGIN
   -- enable the buffer with default size 20000
   dbms_output.enable;
  
   dbms_output.put_line('Hello Reader!');
   dbms_output.put_line('Hope you have enjoyed the tutorials!');
   dbms_output.put_line('Have a great time exploring pl/sql!');
 
   num_lines := 3;
 
   dbms_output.get_lines(lines, num_lines);
 
   FOR i IN 1..num_lines LOOP
      dbms_output.put_line(lines(i));
   END LOOP;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Hello Reader!
Hope you have enjoyed the tutorials!
Have a great time exploring pl/sql!

PL/SQL procedure successfully completed.

PL/SQL - Object Oriented

PL/SQL allows defining an object type, which helps in designing object-oriented database in Oracle. An object type allows you to crate composite types. Using objects allow you implementing real world objects with specific structure of data and methods for operating it. Objects have attributes and methods. Attributes are properties of an object and are used for storing an object's state; and methods are used for modeling its behaviors.
Objects are created using the CREATE [OR REPLACE] TYPE statement. Below is an example to create a simple address object consisting of few attributes:

CREATE OR REPLACE TYPE address AS OBJECT
(house_no varchar2(10),
 street varchar2(30),
 city varchar2(20),
 state varchar2(10),
 pincode varchar2(10)
);
/

When the above code is executed at SQL prompt, it produces the following result:

Type created.

Let's create one more object customer where we will wrap attributes and methods together to have object oriented feeling:

CREATE OR REPLACE TYPE customer AS OBJECT
(code number(5),
 name varchar2(30),
 contact_no varchar2(12),
 addr address,
 member procedure display
);
/

When the above code is executed at SQL prompt, it produces the following result:

Type created.

Instantiating an Object

Defining an object type provides a blueprint for the object. To use this object, you need to create instances of this object. You can access the attributes and methods of the object using the instance name and the access operator (.) as follows:

DECLARE
   residence address;
BEGIN
   residence := address('103A', 'M.G.Road', 'Jaipur', 'Rajasthan','201301');
   dbms_output.put_line('House No: '|| residence.house_no);
   dbms_output.put_line('Street: '|| residence.street);
   dbms_output.put_line('City: '|| residence.city);
   dbms_output.put_line('State: '|| residence.state);
   dbms_output.put_line('Pincode: '|| residence.pincode);
END;
/

When the above code is executed at SQL prompt, it produces the following result:

House No: 103A
Street: M.G.Road
City: Jaipur
State: Rajasthan
Pincode: 201301

PL/SQL procedure successfully completed.

Inheritance for PL/SQL Objects:

PL/SQL allows creating object from existing base objects. To implement inheritance, the base objects should be declared as NOT FINAL. The default is FINAL.
The following programs illustrate inheritance in PL/SQL Objects. Let us create another object named TableTop which is inheriting from the Rectangle object. Creating the base rectangle object:

CREATE OR REPLACE TYPE rectangle AS OBJECT
(length number,
 width number,
 member function enlarge( inc number) return rectangle,
 NOT FINAL member procedure display) NOT FINAL
/

When the above code is executed at SQL prompt, it produces the following result:

Type created.

Creating the base type body:

CREATE OR REPLACE TYPE BODY rectangle AS
   MEMBER FUNCTION enlarge(inc number) return rectangle IS
   BEGIN
      return rectangle(self.length + inc, self.width + inc);
   END enlarge;

   MEMBER PROCEDURE display IS
   BEGIN
      dbms_output.put_line('Length: '|| length);
      dbms_output.put_line('Width: '|| width);
   END display;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Type body created.

Creating the child object tabletop:

CREATE OR REPLACE TYPE tabletop UNDER rectangle
(  
   material varchar2(20);
   OVERRIDING member procedure display
)
/

When the above code is executed at SQL prompt, it produces the following result:

Type created.

Creating the type body for the child object tabletop:

CREATE OR REPLACE TYPE BODY tabletop AS
OVERRIDING MEMBER PROCEDURE display IS
BEGIN
   dbms_output.put_line('Length: '|| length);
   dbms_output.put_line('Width: '|| width);
   dbms_output.put_line('Material: '|| material);
END display;
/

When the above code is executed at SQL prompt, it produces the following result:

Type body created.

Using the tabletop object and its member functions:

DECLARE
   t1 tabletop;
   t2 tabletop;
BEGIN
   t1:= tabletop(20, 10, 'Wood');
   t2 := tabletop(50, 30, 'Steel');
   t1.display;
   t2.display;
END;
/

When the above code is executed at SQL prompt, it produces the following result:

Length: 20
Width: 10
Material: Wood
Length: 50
Width: 30
Material: Steel

PL/SQL procedure successfully completed.

Abstract Objects in PL/SQL

The NOT INSTANTIABLE clause allows you to declare an abstract object. You cannot use an abstract object as it is; you will have to create a subtype or child type of such objects to use its functionalities.
For example,

CREATE OR REPLACE TYPE rectangle AS OBJECT
(length number,
 width number,
 NOT INSTANTIABLE NOT FINAL MEMBER PROCEDURE display) 
 NOT INSTANTIABLE NOT FINAL
/

When the above code is executed at SQL prompt, it produces the following result:

Type created.

SQL and PL/SQL Interview Questions- Part 2 - New question set 2013

SQL and PL/SQL Interview Questions- Part 2

Q.Explain the usage of WHERE CURRENT OF clause in cursors ?
WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers

Q.In a Distributed Database System Can we execute two queries simultaneously ? Justify ?
When 2 people are using DRL command it is possible to execute multiple queries simultaneously.
When we are performing DML operation (update,delete) exclusive lock will be applied on specific record so, DML operation is not possible.
As Distributed database system based on 2 phase commit,one query is independent of 2 nd query so of course we can run.

Q.Can Commit,Rollback ,Savepoint be used in Database Triggers?If yes than HOW? If no Why?With Reasons

we cannot commit inside a trigger.
As we all know that when a dml is complete one can issue a commit.
A trigger if created is fired before the dml completes.
so we cannot commit intermediately.

Q.What will the Output for this Coding?
Declare
Cursor c1 is select * from emp FORUPDATE;
Z c1%rowtype;
Begin
Open C1;
Fetch c1 into Z;
Commit;
Fetch c1 in to Z;
end;
By declaring this cursor we can update the table emp through z,means wo not need to write table name for updation,it may be only by "z".

Q.How we can create a table through procedure ?
You can create table from procedure using Execute immediate command.

Q.What are two parts of package ?
package has two parts
1.Package specification
2.Package body
In the specification,where we declare variable,function,procedure
that is global to the package and local to the schema.
package body contains the defination of the function,procedure.we can also declare private function and procedure which is not accessble
out side the package.
The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY. Package Specification contains declarations that are global to the packages and local to the schema.
Package Body contains actual procedures and local declaration of the procedures and cursor declarations.

Q.The most important DDL statements in SQL are?
CREATE TABLE - creates a new database table
ALTER TABLE - alters (changes) a database table
DROP TABLE - deletes a database table
CREATE INDEX - creates an index (search key)
DROP INDEX - deletes an index

Q.What is difference between a Cursor declared in a procedure and Cursor declared in a package specification ?
A cursor declared in a package specification is global and can be accessed by other procedures or procedures in a package.
A cursor declared in a procedure is local to the procedure that can not be accessed by other procedures.

Q.What is the basic structure of PL/SQL ?
PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.

Q.What is Correlated Subquery?
Correlated Subquery is a subquery that is evaluated once for each row processed by the parent statement. Parent statement can be Select, Update or Delete. Use CRSQ to answer multipart questions whose answer depends on the value in each row processed by parent statement.

Q.Write the order of precedence for validation of a column in a table ?
I. done using Database triggers.
ii. done using Integarity Constraints.
I & ii.
Exception
First column should be validated by constraints and then Triggers

Q.What are two virtual tables available during database trigger execution ?
The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only available.
For triggers related to DELETE only OLD.column_name values only available.
Two tables are: OLD and NEW.
Insert Trigger :
OLD - no value.
NEW - inserted value.
UPDATE TRIGGER -
OLD- old value.
NEW- new updated value.
DELETE TRIGGER -
OLD - old value.
NEW - no value.

Q.The SELECT INTO Statement is most often used to create backup copies of tables or for archiving records?
SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source
SELECT column_name(s) INTO newtable [IN externaldatabase] FROM source WHERE column_name operator value.

Q.What is Data types?
Max. columns in a table is 255. Max. Char size is 255, Long is 64K & Number is 38 digits.
Cannot Query on a long column.
Char, Varchar2 Max. size is 2000 & default is 1 byte.
Number(p,s) p is precision range 1 to 38, s is scale -84 to 127.
Long Character data of variable length upto 2GB.
Date Range from Jan 4712 BC to Dec 4712 AD.
Raw Stores Binary data (Graphics Image & Digitized Sound). Max. is 255 bytes.
Mslabel Binary format of an OS label. Used primarily with Trusted Oracle.

Q.What is Pragma EXECPTION_INIT? Explain the usage?
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error. To get an error message of a specific oracle error.
e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)

Q.What is a cursor ? Why Cursor is required ?
The oracle server uses works areas
called private sql area.Here all the DML statement is executed and to processing statement.basically
it's a implicit cursor.
there are two types of cursor
1.Implicit cursor.
2.Explicit cursor.
Implicit cursor is open for all DML statement.after execute the statement cursor is atomatically closed.
Explicit cursor is created by programmer.
explicit cursor is needed when
query returns more than one rows.
In that case,programmer creates
explicit cursor.open the cursor.
then fetch the value from the active set.
after fetching all the value,
cursor is closed by programmer.

Q.Explain the usage of WHERE CURRENT OF clause in cursors?
WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers

Q.What is the basic structure of PL/SQL?
PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.

Q.Who to put a unique constraint on column if duplicate data is already present in that column?
If duplicate data is already there then instead of putting unique constraint on one column, put unique constraint on two or more columns.

Q.What is SET?
SET command changes the system variables affecting the report environment.

Q.What is Locking?
Locking are mechanisms intended to prevent destructive interaction between users accessing data. Locks are used to achieve.

Q.Explain the usage of WHERE CURRENT OF clause in cursors?
WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers

Q.The INSERT INTO Statements in SQL?
INSERT INTO table_name VALUES (value1, value2,....)
INSERT INTO table_name (column1, column2,...) VALUES (value1, value2,....)

Q.What is the basic structure of PL/SQL?
PL/SQL uses block structure as its basic structure. Anonymous blocks or nested blocks can be used in PL/SQL.

Q.What is difference between a Cursor declared in a procedure and Cursor declared in a package specification?
A cursor declared in a package specification is global and can be accessed by other procedures or procedures in a package.
A cursor declared in a procedure is local to the procedure that can not be accessed by other procedures.

Q.I can not see the answer of the pl/cql code like addition of two no.s. afterall i write dbms_output.put_line('addition is'|| c). Only the line 'PL/SQL procedure successfully completed.' is showing when i end the code by /
before executing the procedure,
set serveroutput on;

Q.Where the Pre_defined_exceptions are stored?
In the standard package.
Procedures, Functions & Packages ;

Q.What is difference between a PROCEDURE & FUNCTION?
A FUNCTION is always returns a value using the return statement.
A PROCEDURE may return one or more values through parameters or may not return at all.

Q.How can a function retun more than one value in oracle with proper example?
yes we can use objects, arrays to return more than one value

Q.How to know the last executed procedure?
Execute procedure name (parameter1,parameter2)
Select timestamps, owner, obj_name, action_name from dba_audit_trail;this statement gives last executed time for procedure , function & package.

Q.Name the tables where characteristics of Package, procedure and functions are stored ?
User_objects, User_Source and User_error.

Q.1)What is the starting "oracle error number"?
2)What is meant by forward declaration in functions?
One must declare an identifier before referencing it. Once it is declared it can be referred even before defining it in the PL/SQL. This rule applies to function and procedures also

Q.What is difference between a PROCEDURE & FUNCTION ?
A FUNCTION is always returns a value using the return statement.
A PROCEDURE may return one or more values through parameters or may not return at all.
In case of function,it must have
return type.
In case of procedure,it may or may n't have return type.
In case of function, only it takes IN parameters
IN case of procedure
only it take IN,OUT,INOUT parameters..

Q.Give the structure of the function ?
FUNCTION name (argument list .....) Return datatype is
local variable declarations
Begin
executable statements
Exception
execution handlers
End;

Q.What is Union?
Union is the product of two or more tables. Which is removed duplicate values from the query.
Union is the product of two or more tables.

Q.What are the components of a PL/SQL Block ?
Declare
variable declaration
Begin
Execution part
Exception
Exception handling
End;
Declarative part, Executable part and Exception part.
Datatypes PL/SQL

Q.What are two virtual tables available during database trigger execution?
The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only available.
For triggers related to DELETE only OLD.column_name values only available.

Q.What is Synonyms?
Synonyms is the alias name for table, views, sequences & procedures and are created for reasons of Security and Convenience.
Two levels are Public - created by DBA & accessible to all the users. Private - Accessible to creator only. Advantages are referencing without specifying the owner and Flexibility to customize a more meaningful naming convention.

Q.What is COMPUTE?
command control computations on subsets created by the BREAK command.When we are trying to determine the sum of some columns in a result set we can use Compute. This function is used for reporting purpose.

Q.What is the use of CASCADE CONSTRAINTS?
Integrity key is violated when one tried to delete parent key value when foreign key value.
A parent key value can only be deleted after foreign key value.
Cascade constraints has dual purpose.
1.Alter table command can be issued with "ON DELETE CASCADE"
When this is done one can run delete command with cascade constriaint to delete parent key value.
2.To drop a table that has parent values.
With cascade constraint,foreign key constraint on child table and parent table is dropped.The child table still exits.
When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.

Q.The Update Statement in SQL.
UPDATE table_name SET column_name = new_value WHERE column_name = some_value

Q.How Can i convert the Columns In to Row in a oracle Select Query ?
By using matrix report query
Example:
select job,sum(DECODE(deptno,10,sal)) "d10_sal",
sum(DECODE(deptno,20,sal)) "d20_sal",
sum(DECODE(deptno,30,sall)) "d30_sal",
sum(sal) "total"
from emp group by job;

Q.What are two virtual tables available during database trigger execution?
The table columns are referred as OLD.column_name and NEW.column_name.
For triggers related to INSERT only NEW.column_name values only available.
For triggers related to UPDATE only OLD.column_name NEW.column_name values only available.
For triggers related to DELETE only OLD.column_name values only available.

Q.What is difference between % ROWTYPE and TYPE RECORD?
% ROWTYPE is to be used whenever query returns a entire row of a table or view.
TYPE rec RECORD is to be used whenever query returns columns of different
table or views and variables.
E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %type);
e_rec emp% ROWTYPE
cursor c1 is select empno,deptno from emp;
e_rec c1 %ROWTYPE.
One more point : When we have a variable of typer RECORD we have declare additional variables but with %rowtype, we can only have the fields that are present in the table

Q.How can a function retun more than one value in oracle with proper example?
yes we can use objects, arrays to return more than one value

Q.Write a PL/SQL block to list all the managers
DECLARE
LV_MANAGER_NAME VARCHAR2(100);
LN_COUNT NUMBER;
CURSOR C1 AS
SELECT * FROM EMP_DETAILS WHERE DESIGNATION = 'MANAGER'
BEGIN
LN_COUNT := 0;
FOR EMPDET IN C1 LOOP
LV_MANAGER_NAME := EMPDET.EMP_NAME;
LN_COUNT = LN_COUNT+1;
DBMS_OUTPUT.PUT_LINE('MANAGER '||LN_COUNT||' -> '||LV_MANAGER_NAME);
END LOOP;
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.PUT_LINE('EXCEPTION OCCURED:'||SQLERRM);
END;

Q.Explian rowid,rownum?What are the pseduocolumns we have?
ROWID - Hexa decimal number each and every row having unique.Used in searching
ROWNUM - It is a integer number also unique for sorting Normally TOP N Analysys.
Other Psudo Column are
NEXTVAL,CURRVAL Of sequence are some examples

Q.What is Pragma EXECPTION_INIT ? Explain the usage ?
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error. To get an error message of a specific oracle error.
e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)

Q.Write a PL/SQL block to update the salary of an employee whose empno is 7839 and print the message as ?Record Updated?.
begin
update employee(tablename) set salary=(salary)*o.1 where empno=7839;
dbms_output.put_line('record updated');
end;
declare
a exception;
begin
update emp set sal=(sal*0.1) where empno=7839;
if sql%rowcount>0 then
dbms_output.put_line(sql%rowcount ||' records are updated' );
else
raise a;
end if;
exception
when a then
dbms_output.put_line('records are not updated');
end;

Q.How packaged procedures and functions are called from the following?
a.Stored procedure or anonymous block
b.an application program such a PRC *C, PRO* COBOL
c.SQL *PLUS
a.PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b.BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c.EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any out/in-out parameters. A function can not be called.

Q.What is TTITLE and BTITLE?
TTITLE & BTITLE are commands to control report headings & footers.

Q.Is it possible to use Transaction control Statements such a ROLLBACK or COMMIT in Database Trigger ? Why
It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.
No, we can not use Commit or Rollback, within a trigger. To understand, take one simple example...
Suppose two persons are using one common table and they both have written trigger on that table. If in the first trigger we are using commit/rollback, then the second use would get some unwanted result.
That is the reason, why we don't use Commit/Rollback in Triggers.
Yeah. If some type of failure/ breakdown occurs, in that case Oracle automatically Rollback the data.

Q.select seq1.nextval from dual
It returns two values at a time.
100
100
Is it possible?If so how?
select naw1.nextval,naw1.currval into n from dual;
Well, in a way it is:
SQL> create sequence foo_seq start with 100 increment by 3;
Sequence created.
SQL> create table dual (dummy varchar2(1));
Table created.
SQL> insert into dual values ('X');
1 row created.
SQL> insert into dual values ('Y');
1 row created.
SQL> commit;
Commit complete.
SQL> select foo_seq.nextval from dual;
NEXTVAL
----------
100
103
SQL>
It's a mean trick to play on developers.

Q.What will the Output for this Coding>
Declare
Cursor c1 is select * from emp FORUPDATE;
Z c1%rowtype;
Begin
Open C1;
Fetch c1 into Z;
Commit;
Fetch c1 in to Z;
end;
By declaring this cursor we can update the table emp through z,means wo not need to write table name for updation,it may be only by "z".
By issuing the TCL like commit or rollback, the cursor will be closed automatically, you cannot fetch again.


Q.How to avoid using cursors? What to use instead of cursor and in what cases to do so?
Just use subquery in for clause
ex:For emprec in (select * from emp)
loop
dbms_output.put_line(emprec.empno);
end loop;
no exit statement needed
implicit open,fetch,close occurs

Q.What are the return values of functions SQLCODE and SQLERRM?
SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE.

Q.Explian rowid, rownum?what are the psoducolumns we have?
ROWID - Hexa decimal number each and every row having unique.Used in searching.
ROWNUM - It is a integer number also unique for sorting Normally TOP N Analysys.
Other Psudo Column are
NEXTVAL,CURRVAL Of sequence are some exampls
psudo columns are default columns provided by oracle

Q.Give the Types of modules in a form?
Form
Menu
Library

Q.What happens if a procedure that updates a column of table X is called in a database trigger of the same table?
Mutation of table occurs.

Q.Can we declare a column having number data type and its scale is larger than pricesion
ex: column_name NUMBER(10,100),
column_name NUMBAER(10,-84)
Yes,we can declare a column with above condition.table created successfully.
yes, 100 is the total size and 10 is included in 100

Q.What is SQL Integrity?
Assures database data and structures reflects all changes made to them in the correct sequence. Locks ensure data integrity and maximum concurrent access to data. Commit statement releases all locks. Types of locks are given below.
Data Locks protects data i.e. Table or Row lock.
Dictionary Locks protects the structure of database object i.e. ensures table's structure does not change for the duration of the transaction.
Internal Locks & Latches protects the internal database structures. They are automatic.
Exclusive Lock allows queries on locked table but no other activity is allowed.
Share Lock allows concurrent queries but prohibits updates to the locked tables.
Row Share allows concurrent access to the locked table but prohibits for a exclusive table lock.
Row Exclusive same as Row Share but prohibits locking in shared mode.
Shared Row Exclusive locks the whole table and allows users to look at rows in the table but prohibit others from locking the table in share or updating them.
Share Update are synonymous with Row Share.

Q.What are the components of a PL/SQL block ?
components of PL/SQL are:
declare:
(optional) variable declare
Begin:
(Mandatory)Procedural statement
Exception:
(optional)
error to be trapped
End:
(Mandatory)
So BEGIN and END are required in PL/SQL block

Q.What is difference between % ROWTYPE and TYPE RECORD ?
% ROWTYPE is to be used whenever query returns a entire row of a table or view.
TYPE rec RECORD is to be used whenever query returns columns of different table or views and variables.
E.g. TYPE r_emp is RECORD (eno emp.empno% type,ename emp ename %type);
e_rec emp% ROWTYPE
cursor c1 is select empno,deptno from emp;
e_rec c1 %ROWTYPE.

Q.What are the datatypes a available in PL/SQL ?
1.Character Datatypes:
char(size), nchar(size), varchar2(size), nvarchar2(size),long, raw, longraw
2.Numeric Datatypes number(p,s), numeric(p,s),float, dec(p,s), decimal(p,s),integer, int, smallint,real, double precision
3.Date/Time Datatypes:
date, timestamp, timestamp with local time zone, timestamp with time zone, interval year to month, interval day to second
4.LOB data types:
bfile,blob,clob,nclob
5. Rowid Data types:
rowid,urowid
Some scalar data types such as NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN. Some composite data types such as RECORD & TABLE.

Q.Explian rowid, rownum? what are the psoducolumns we have ?
ROWID - Hexa decimal number each and every row having unique.Used in searching.
ROWNUM - It is a integer number also unique for sorting Normally TOP N Analysys.
Other Psudo Column are NEXTVAL,CURRVAL Of sequence are some examples
psudo columns are default columns provided by oracle
both rowid n rownum are psedocolumns, but
rowid- is physical address for each record in the memory.
rownum gives the numbering to rows returned by sql select statement.

Q.What is Indexes?
Indexes are optional structures associated with tables used to speed query execution and/or guarantee uniqueness. Create an index if there are frequent retrieval of fewer than 10-15% of the rows in a large table and columns are referenced frequently in the WHERE clause. Implied tradeoff is query speed vs. update speed. Oracle automatically update indexes. Concatenated index max. is 16 columns.

Q.What is Raise_application_error?
Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue an user_defined error messages from stored sub-program or database trigger.

Q.State the difference between implict and explict cursors?
Collapse/Expand Answer of Question State the difference between implict and explict cursors?
Implicit Cursor are declared and used by the oracle internally. whereas the explicit cursors are declared and used by the user. more over implicitly cursors are no need to declare oracle creates and process and closes autometically. the explicit cursor should be declared and closed by the user.
Implicit cursors are used for single row query whereas explicit cursor is used for multiple row query
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Please send that collection to iq@GlobalGuideline.Com along with the category and sub category information

Q.What are the modes of parameters that can be passed to a procedure?
IN,OUT,IN-OUT parameters.

Q.What will happen after commit statement?
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.

Q.How many types of database triggers can be specified on a table? What are they?
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.

Q.What will be the Output for this Coding
Declare
Cursor c1 is select * from emp FORUPDATE;
Z c1%rowtype;
Begin
Open C1;
Fetch c1 into Z;
Commit;
Fetch c1 in to Z;
By declaring this cursor we can update the table emp through z,means wo not need to write table name for updation,it may be only by "z".
By issuing the TCL like commit or rollback, the cursor will be closed automatically, you cannat fetch again.

Q.What will happen after commit statement?
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.

Q.What is an oracle stored procedure?

A stored procedure is a sequence of statements that perform specific function.

Q.Explain the usage of WHERE CURRENT OF clause in cursors?

WHERE CURRENT OF clause in an UPDATE,DELETE statement refers to the latest row fetched from a cursor. Database Triggers

SQL and PL SQL Interview Questions - New Question Set 2013

Q.What is a stored procedure ?

A stored procedure is a sequence of statements that perform specific function.
A stored procedure is a named pl/sql block which performs an action.It is stored in the database as a schema object and can be repeatedly executed.It can be invoked, parameterised and nested.

Q.What is SQL*Loader?

SQL*Loader is a product for moving data in external files into tables in an Oracle database. To load data from external files into an Oracle database, two types of input must be provided to SQL*Loader : the data itself and the control file. The control file describes the data to be loaded. It describes the Names and format of the data files, Specifications for loading data and the Data to be loaded (optional). Invoking the loader sqlload username/password controlfilename <options>.

Q.What are the two parts of a procedure ?

the above person have answerd wrong. Or rather the question may be wrong. It should be packages instead of procedures. What are the 2 parts of package ? But the question is what are the 2 parts for procedue!!!
Procedure Specification and Procedure Body.

Q.What is Date Functions?
Date Functions are ADD_MONTHS, LAST_DAY, NEXT_DAY, MONTHS_BETWEEN & SYSDATE.

Q.What is NVL?
NVL: Null value function converts a null value to a non-null value for the purpose of evaluating an expression. Numeric Functions accept numeric I/P & return numeric values. They are MOD, SQRT, ROUND, TRUNC & POWER.

Q.What is Intersect?
Intersect is the product of two tables listing only the matching rows.

Q.How to know the last executed procedure?
Execute procedure name (parameter1,parameter2)
Select timestamps, owner, obj_name, action_name from dba_audit_trail;this statement gives last executed time for procedure , function & package.

Q.What are the Restrictions on Cursor Variables?
Currently, cursor variables are subject to the following restrictions:You cannot declare cursor variables in a package spec. For example, the following declaration is not allowed:CREATE PACKAGE emp_stuff AS TYPE EmpCurTyp IS REF CURSOR RETURN emp%ROWTYPE; emp_cv EmpCurTyp; -- not allowedEND emp_stuff;You cannot pass cursor variables to a procedure that is called through a database link.If you pass a host cursor variable to PL/SQL, you cannot fetch from it on the server side unless you also open it there on the same server call.You cannot use comparison operators to test cursor variables for equality, inequality, or nullity.You cannot assign nulls to a cursor variable.Database columns cannot store the values of cursor variables. There is no equivalent type to use in a CREATE TABLE statement.You cannot store cursor variables in an associative array, nested table, or varray.Cursors and cursor variables are not interoperable; that is, you cannot use one where the other is expected. For example, you cannot
reference a cursor variable in a cursor FOR loop

Q.What is Minus?
Minus is the product of two tables listing only the non-matching rows.

Q.What are the cursor attributes used in PL/SQL?
% ISOPEN - To check whether cursor is open or not
% ROWCOUNT - Number of rows fetched/updated/deleted.
% FOUND - To check whether cursor has fetched any row. True if rows are fetched.
% NOT FOUND - To check whether cursor has fetched any row. True if no rows are featched.
These attributes are proceeded with SQL for Implicit Cursors and with Cursor name for Explicit Cursors.

Q.What is Consistency?
consistency: states that until commit the data will not be reflected to other users,in order to maintain proper consistency.
consider a example: if user A transfer money to user B. The changes are updates in A account (debit) but until it will be updated in B (credit) too till then others will not be able to see the debit of A. when debit to A and credit to B happen then one can see the updates hence maintain consistency

Q.What are % TYPE and % ROWTYPE? What are the advantages of using these over data types?
% TYPE provides the data type of a variable or a database column to that variable.
% ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.
The advantages are : I. Need not know about variable's data type
ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly.

Q.What will the Output for this Coding
Declare
Cursor c1 is select * from emp FORUPDATE;
Z c1%rowtype;
Begin
Open C1;
Fetch c1 into Z;
Commit;
Fetch c1 in to Z;
end;
By declaring this cursor we can update the table emp through z,means wo not need to write table name for updation,it may be only by "z".
By issuing the TCL like commit or rollback, the cursor will be closed automatically, you cannat fetch again. You will get an error if you

Q.What is Commit?
Commit is an event that attempts to make data in the database identical to the data in the form. It involves writing or posting data to the database and committing data to the database. Forms check the validity of the data in fields and records during a commit. Validity check are uniqueness, consistency and db restrictions.

Q.Give the structure of the function?
FUNCTION name (argument list .....) Return datatype is
local variable declarations
Begin
executable statements
Exception
execution handlers
End;

Q.What is a cursor ? Why Cursor is required?
Cursor is a named private SQL area from where information can be accessed. Cursors are required to process rows individually for queries returning multiple rows.

Q.If the application is running very slow? At what points you need to go about the database in order to improve the performance?
For improving performance, we need to check the sql statement blocks , because for every sql satement execution transfor to sql engine and come back to plsq engine that process takes more time to process the plsql block.

Q.What are advantages fo Stored Procedures?
Extensibility,Modularity, Reusability, Maintainability and one time compilation.

Q.What is difference b/w stored procedures and application procedures, stored function and application function?
Stored procedures are subprogrammes stored in the database and can be called &executee multiple times wherein an application procedure is the one being used for a particular application same is the way for function.
Both can be executed any number of times. Only difference is that stored procedures/ functions are stored in database in complied format while the application procedures/functions are not in precomplied format and at run time has to be compiled.

Q.What is a cursor ? Why Cursor is required?
Cursor is a named private SQL area from where information can be accessed. Cursors are required to process rows individually for queries returning multiple rows.

Q.State the difference between implicit and explicit cursor's.
Implicit Cursor are declared and used by the oracle internally. whereas the explicit cursors are declared and used by the user. more over implicitly cursors are no need to declare oracle creates and process and closes autometically. the explicit cursor should be declared and closed by the user.

Q.How to avoid using cursors? What to use instead of cursor and in what cases to do so?
just use subquery in for clause
ex:
for emprec in (select * from emp)
loop
dbms_output.put_line(emprec.empno);
end loop;
no exit statement needed
implicit open,fetch,close occurs

Q.What is pl/sql?what are the advantages of pl/sql?
PL/SQL(a product of Oracle) is the 'programming language' extension of sql.
It is a full-fledged language although it is specially designed for database centric activities.

Q.How to disable multiple triggers of a table at at a time?
ALTER TABLE<TABLE NAME> DISABLE ALL TRIGGER

Q.How many types of database triggers can be specified on a table ? What are they ?
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.

Q.Explain how procedures and functions are called in a PL/SQL block ?
Function can be called from SQL query + explicitly as well
e.g 1)select empno,salary,fn_comm(salary)from employee;
2)commision=fn_comm(salary);
Procedure can be called from begin-end clause.
e.g.
Begin
(
proc_comm(salary);
)
end
Function is called as part of an expression.
sal := calculate_sal ('a822');
procedure is called as a PL/SQL statement
calculate_bonus ('A822');

Q.What will happen after commit statement ?
Cursor C1 is
Select empno,
ename from emp;
Begin
open C1; loop
Fetch C1 into
eno.ename;
Exit When
C1 %notfound;-----
commit;
end loop;
end;
The cursor having query as SELECT .... FOR UPDATE gets closed after COMMIT/ROLLBACK.
The cursor having query as SELECT.... does not get closed even after COMMIT/ROLLBACK.

Q.What happens if a procedure that updates a column of table X is called in a database trigger of the same table ?
Trigger will be called... Based on the event what trigger as to do. if trigger is also doing the same update statment then Mutating Table occurs. if trigger is not doing any DML statment nothing happens just Trigger will be called..

Q.Can we declare a column having number data type and its scale is larger than pricesion
ex: column_name NUMBER(10,100),
column_name NUMBAER(10,-84)
Yes,
we can declare a column with above condition.
table created successfully.

Q.The IN operator may be used if you know the exact value you want to return for at least one of the columns.
SELECT column_name FROM table_name WHERE column_name IN (value1,value2,..)

Q.What is SQL Deadlock?
Deadlock is a unique situation in a multi user system that causes two or more users to wait indefinitely for a locked resource. First user needs a resource locked by the second user and the second user needs a resource locked by the first user. To avoid dead locks, avoid using exclusive table lock and if using, use it in the same sequence and use Commit frequently to release locks.

Q.Where the Pre_defined_exceptions are stored ?
In the standard package.
Procedures, Functions & Packages ;

Q. Below is the table
city gender name
delhi male a
delhi female b
mumbai male c
mumbai female d
delhi male e
I want the o/p as follows:
male female
delhi 2 1
mumbai 1 1
Please help me in writing the query that can yield the o/p mentioned above?
select city, sum(decode(gender,'male',1,0)) Male_cnt, sum(gender,'female',1,0) female_cnt
from table_name
group by city
select a.city,a.male,b.female from
(select city,count(gender) male from city where gender='m'group by city,gender)a
join
(select city,count(gender) female from city where gender='f' group by city,gender)b
on a.city=b.city

Q.What is Sequences?
Sequences are used for generating sequence numbers without any overhead of locking. Drawback is that after generating a sequence number if the transaction is rolled back, then that sequence number is lost

Q.What are % TYPE and % ROWTYPE ? What are the advantages of using these over datatypes?
% TYPE provides the data type of a variable or a database column to that variable.
% ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.
The advantages are : I. Need not know about variable's data type
ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly.

Q.What is Mutating SQL Table?
Mutating Table is a table that is currently being modified by an Insert, Update or Delete statement. Constraining Table is a table that a triggering statement might need to read either directly for a SQL statement or indirectly for a declarative Referential Integrity constraints. Pseudo Columns behaves like a column in a table but are not actually stored in the table. E.g. Currval, Nextval, Rowid, Rownum, Level etc.

Q.What is PL/SQL table ?
Objects of type TABLE are called "PL/SQL tables", which are modeled as (but not the same as) database tables, PL/SQL tables use a primary PL/SQL tables can have one column and a primary key.
Cursors
PL/SQL tables are PL/SQL?s way of providing arrays. Arrays are like tem-porary
tables in memory and thus are processed very quickly. It is impor-tant
for you to realize that they are not database tables, and DML
statements cannot be issued against them. This type of table is indexed
by a binary integer counter (it cannot be indexed by another type of
number) whose value can be referenced using the number of the index.
Remember that PL/SQL tables exist in memory only, and therefore don't
exist in any persistent way, disappearing after the session ends.
A PL/SQL TABLE DECLARATION
There are two steps in the declaration of a PL/SQL table. First, you must define the table structure using the TYPE statement. Second, once a table type is created, you then declare the actual table.
FOR EXAMPLE
DECLARE
-- Table structure definition
TYPE NameType IS TABLE OF
Customer.name_name%TYPE
INDEX BY BINARY_INTEGER;
-- Create the actual table
CnameTab NameType;
KnameTab NameType;
BEGIN
NULL; -- ...
END;

Q.In a Distributed Database System Can we execute two queries simultaneously? Justify?
Yes, Distributed database system based on 2 phase commit,one query is independent of 2 nd query so of course we can run.

Q.What are the modes of parameters that can be passed to a procedure ?
IN parameter is the default mode which acts as a constant inside calling environment.value passed in this parameter can not be changed.OUT parameter mode is used to pass value from calling environment into main block,here we can change the value.It acts as a variable inside calling environment.
INOUT parameter mode which pass value into calling environment and will get the value back in main block.
IN parameter mode uses call by reference method to pass value from formal parameter to actual parameter.
OUT & INOUT parameter mode uses call by value method to pass values.
IN,OUT,IN-OUT parameters.

Q.Name the tables where characteristics of Package, procedure and functions are stored?
User_objects, User_Source and User_error.

Q.How many types of database triggers can be specified on a table? What are they?
Insert Update Delete
Before Row o.k. o.k. o.k.
After Row o.k. o.k. o.k.
Before Statement o.k. o.k. o.k.
After Statement o.k. o.k. o.k.
If FOR EACH ROW clause is specified, then the trigger for each Row affected by the statement.
If WHEN clause is specified, the trigger fires according to the returned Boolean value.

Q.How can a function retun more than one value in oracle with proper example?
Basically as per property of function it has to return one value. So the other values can be returned from the out parameter of the function.
But its advised if you want more that one return value go for procedure however function will also yield the same result.

Q.Explain If the entire disk is corrupted how will you and what are the steps to recover the database?
if the entire disk is corrupted and no backup is there don nothing sit and relax their is no possibility of recovery ...a backup is required for restoration and for recovery redo log and archive logs.
Once if you have theses than think of recovering ..a dba should always plan for the recovery scenario depending upon the criticality of the database.oracle provides 0% data loss facilty through data guard and online backup .its dba who has to decide.

Q.What is Rollback?
Rollback causes work in the current transaction to be undone.

Q.What is a cursor for loop ?
Cursor for loop implicitly declares %ROWTYPE as loop index,opens a cursor, fetches rows of values from active set into fields in the record and closes when all the records have been processed.
eg. FOR emp_rec IN C1 LOOP
salary_total := salary_total +emp_rec sal;
END LOOP;

Q.How to sort the rows in SQL?
Sort the Rows:
SELECT column1, column2, ... FROM table_name ORDER BY columnX, columnY, ..
SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC
SELECT column1, column2, ... FROM table_name ORDER BY columnX DESC, columnY ASC1.
select column1,column2,column3 from table1
where
column1>10
order by 1,3,2;
Inthis case it sorts based on the columns' position in the select query i.e. in the above query it will sort first based on column1 then on column3 and then by column2. By default the sort is in ascending order, if you want it to be in descending order, you need to specify the key word DESC in ORDER BY clause.
2.select * from emp order by eno desc;
You can sort your results based on any column in the tables because you are select all the columns.
3.select eno,ename from emp order by deptno;
This is wrong because the column deptno is not present in the select clause.

Q.What is Pragma EXECPTION_INIT? Explain the usage?
The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error. To get an error message of a specific oracle error.
e.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number

Q.What's the use of dyanamic sql in oracle?
Dynamic SQL enables you to write programs that reference SQL statements whose full text is not known until runtime.

Q.How we can create a table in PL/SQL block. insert records into it? is it possible by some procedure or function? please give example?
CREATE OR REPLACE PROCEDURE ddl_create_proc (p_table_name IN VARCHAR2)
AS
l_stmt VARCHAR2(200);
BEGIN
DBMS_OUTPUT.put_line('STARTING ');
l_stmt := 'create table '|| p_table_name || ' as (select * from emp )';
execute IMMEDIATE l_stmt;
DBMS_OUTPUT.put_line('end ');
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.put_line('exception '||SQLERRM || 'message'||sqlcode);
END;

Q.What is a JOIN?
JOIN is the form of SELECT command that combines info from two or more tables.
Types of Joins are Simple (Equijoin & Non-Equijoin), Outer & Self join.
Equijoin returns rows from two or more tables joined together based upon a equality condition in the WHERE clause.
Non-Equijoin returns rows from two or more tables based upon a relationship other than the equality condition in the WHERE clause.
Outer Join combines two or more tables returning those rows from one table that have no direct match in the other table.
Self Join joins a table to itself as though it were two separate tables.

Q.what is the starting oracle error number?
what is meant by forward declaration in functions?
One must declare an identifier before referencing it. Once it is declared it can be referred even before defining it in the PL/SQL. This rule applies to function and procedures also.

Q.Can we declare a column having number data type and its scale is larger than pricesion
ex: column_name NUMBER(10,100),
column_name NUMBAER(10,-84)
No, you cant. May be your table might be created successfully but if you try to insert values it will shows you an error.
Numeric or Value Error
NUMBER (p,s)
p- precision, which is the total size of digits
s- scale , which represents the total number of digits that are present to the right side of the decimal.
s should be strictly less than p. If I am missing somthing. Please fill me in.
Yes,we can declare a column with above condition.table created successfully.
yes, 100 is the total size and 10 is included in 100

Q.Is it possible to use Transaction control Statements such a ROLLBACK or COMMIT in Database Trigger? Why?
It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.
yes WE can use COMMIT and ROLLBACK triggers, but by using PRAGAMA AUTONAMOUS_TRANSATIONS. Now the transation treated as a autonomous tansation.

Q.What is COLUMN?
COLUMN command define column headings & format data values.

Q.SELECT statements in SQL?
SELECT column_name(s) FROM table_name
SELECT DISTINCT column_name(s) FROM table_name
SELECT column FROM table WHERE column operator value
SELECT column FROM table WHERE column LIKE pattern
SELECT column,SUM(column) FROM table GROUP BY column
SELECT column,SUM(column) FROM table GROUP BY column HAVING SUM(column) condition value
Note that single quotes around text values and numeric values should not be enclosed in quotes. Double quotes may be acceptable in some databases.

Q.What is the Delete Statements in SQL?
Delete statement in SQL is used to delete partial/all data.
Especially delete statement is useful in case of partial delete depending upon our criterias otherwise use TRUNCATE to delete whole data from table.
When delete command fires then:
1) Triggers will fire (If created on that table)
2) This will not auto commit changes made So there is one chance to rollback.
3) If u delete whole data then HWM (Highest Water Mark) will not change which gets changed in case of Truncate.

Q.What is Posting?
Posting is an event that writes Inserts, Updates & Deletes in the forms to the database but not committing these transactions to the database.

Q.Where the Pre_defined_exceptions are stored?
In the standard package.
Procedures, Functions & Packages ;

Q.What are two parts of package?
The two parts of package are PACKAGE SPECIFICATION & PACKAGE BODY. Package Specification contains declarations that are global to the packages and local to the schema.
Package Body contains actual procedures and local declaration of the procedures and cursor declarations.

Q.What are the datatypes a available in PL/SQL?
Some scalar data types such as
NUMBER,
VARCHAR2,
DATE,
CHAR,
LONG,
BOOLEAN.
Some composite data types such as RECORD & TABLE.

Q.What is an Exception? What are types of Exception?
Exception is the error handling part of PL/SQL block. The types are Predefined and user defined. Some of Predefined exceptions are.
CURSOR_ALREADY_OPEN
DUP_VAL_ON_INDEX
NO_DATA_FOUND
TOO_MANY_ROWS
INVALID_CURSOR
INVALID_NUMBER
LOGON_DENIED
NOT_LOGGED_ON
PROGRAM-ERROR
STORAGE_ERROR
TIMEOUT_ON_RESOURCE
VALUE_ERROR
ZERO_DIVIDE
OTHERS.
exception is an identifier and error handling part of pl/sql types := 1)predifined 2) user defined.

Q.Explian rowid, rownum?what are the psoducolumns we have?
ROWID - Hexa decimal number each and every row having unique.Used in searching.
ROWNUM - It is a integer number also unique for sorting Normally TOP N Analysys.
Other Psudo Column are
NEXTVAL,CURRVAL Of sequence are some exampls
psudo columns are default columns provided by oracle

Q.How to avoid using cursors? What to use instead of cursor and in what cases to do so?
Just use subquery in for clause
ex:For emprec in (select * from emp)
loop
dbms_output.put_line(emprec.empno);
end loop;
no exit statement needed
implicit open,fetch,close occurs

Q.what is the starting oracle error number?
what is meant by forward declaration in functions?
One must declare an identifier before referencing it. Once it is declared it can be referred even before defining it in the PL/SQL. This rule applies to function and procedures also
ORA-20000

Q.What are the components of a PL/SQL block?
A set of related declarations and procedural statements is called block.
DECLARE -- declaration section BEGIN -- executable statements -- main section EXCEPTION -- handling possible exceptions -- occuring in the main section END;

Q.What is difference between stored procedures and application procedures,stored function and application function?
Stored procedures are sub programs stored in the database and can be called & execute multiple times where in an application procedure is the one being used for a particular application same is the way for function
Procedure:-
Execute as a PL/SQL
statement,No RETURN clause in
the header,Can return none, one,
or many values,Can contain a RETURN
statement
Function:-Invoke as part of an
expression,Must contain a RETURN
clause in the header,Must return a single value,Must contain at least one RETURN statement

Q.What is Raise_application_error ?
Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue an user_defined error messages from stored sub-program or database
trigger.

Q.What is trigger,cursor,functions in pl-sql and we need sample programs about it?
Trigger is an event driven PL/SQL block. Event may be any DML transaction.
Cursor is a stored select statement for that current session. It will not be stored in the database, it is a logical component.
Function is a set of PL/SQL statements or a PL/SQL block, which performs an operation and must return a value.

Q.How we can create a table in PL/SQL block. insert records into it??? is it possible by some procedure or function?? please give example...
CREATE OR REPLACE PROCEDURE ddl_create_proc (p_table_name IN VARCHAR2)
AS
l_stmt VARCHAR2(200);
BEGIN
DBMS_OUTPUT.put_line('STARTING ');
l_stmt := 'create table '|| p_table_name || ' as (select * from emp )';
execute IMMEDIATE l_stmt;
DBMS_OUTPUT.put_line('end ');
EXCEPTION
WHEN OTHERS THEN
DBMS_OUTPUT.put_line('exception '||SQLERRM || 'message'||sqlcode);
END;

Q.In pl/sql functions what is use of out parameter even though we have return statement.
With out parameters you can get the more than one out values in the calling program. It is recommended not to use out parameters in functions. If you need more than one out values then use procedures instead of functions.

Q.How to debug the procedure ?
You can use DBMS_OUTPUT oracle supplied package or DBMS_DEBUG pasckage.

Q.What is ref cursor?
In PL/SQL ,pointer has a datatype REF X where
REF-Reference
X-class of objects
Cursor Variables has a datatype REF-CURSOR
where Cursor Varibales are like pointers which hold the memory location of some item instead of the item itself.

Q.State the advantage and disadvantage of Cursor?
Advantage :
In pl/sql if you want perform some actions more than one records you should user these cursors only. bye using these cursors you process the query records. you can easily move the records and you can exit from procedure when you required by using cursor attributes.
disadvantage:
using implicit/explicit cursors are depended by sutiation. if the result set is les than 50 or 100 records it is better to go for implicit cursors. if the result set is large then you should use exlicit cursors. other wise it will put burdon on cpu.

Q.What is a database trigger ? Name some usages of database trigger ?
A database triggers is stored PL/SQL program unit associated with a specific database table or view. The code in the trigger defines the action the database needs to perform whenever some database manipulation (INSERT, UPDATE, DELETE) takes place.
Unlike the stored procedure and functions, which have to be called explicitly, the database triggers are fires (executed) or called implicitly whenever the table is affected by any of the above said DML operations.
Till oracle 7.0 only 12 triggers could be associated with a given table, but in higher versions of Oracle there is no such limitation. A database trigger fires with the privileges of owner not that of user
A database trigger has three parts
1. A triggering event
2. A trigger constraint (Optional)
3. Trigger action
A triggering event can be an insert, update, or delete statement or a instance shutdown or startup etc. The trigger fires automatically when any of these events occur A trigger constraint specifies a Boolean expression that must be true for the trigger to fire. This condition is specified using the WHEN clause. The trigger action is a procedure that contains the code to be executed when the trigger fires.
Database trigger is stored PL/SQL program unit associated with a specific database table. Usages are Audit data modifications, Log events transparently, Enforce complex business rules Derive column values automatically, Implement complex security authorizations. Maintain replicate tables.

Q.What are the return values of functions SQLCODE and SQLERRM ?
SQLCODE returns the latest code of the error that has occurred.
SQLERRM returns the relevant error message of the SQLCODE.

Q.How packaged procedures and functions are called from the following?
a. Stored procedure or anonymous block
b. an application program such a PRC *C, PRO* COBOL
c. SQL *PLUS
a.PACKAGE NAME.PROCEDURE NAME (parameters);
variable := PACKAGE NAME.FUNCTION NAME (arguments);
EXEC SQL EXECUTE
b.
BEGIN
PACKAGE NAME.PROCEDURE NAME (parameters)
variable := PACKAGE NAME.FUNCTION NAME (arguments);
END;
END EXEC;
c. EXECUTE PACKAGE NAME.PROCEDURE if the procedures does not have any out/in-out parameters. A function can not be called.

Q.Operators used in SELECT statements are?
= Equal
<> or != Not equal
> Greater than
< Less than
>= Greater than or equal
<= Less than or equal
BETWEEN Between an inclusive range
LIKE Search for a pattern

Q.Give the structure of the procedure ?
basically procedure has three
parts
1.variable declaretion(optional)
2.body(mandetory)
3.Exception(optional)
suppose ex
CREATE OR REPLACEPROCEDURE emp_pro( p_id IN employees.employee_id%TYPE)
IS
v_name employees.last_name%TYPE;
v_mail employees.email%TYPE;
BEGIN
SELECT last_name,email INTO v_name,v_mail FROM employees
WHERE employee_id:=p_id;
DBMS_OUTPUT.PUT_LINE('NAME:'||v_name ||'MAILID:'||v_mail);
END;
/
PROCEDURE name (parameter list.....)
is
local variable declarations
BEGIN
Executable statements.
Exception.
exception handlers
end;

Q.What is SPOOL?
spool command used for printing the out put of the sql statments in a file. Eg.
spool /tmp/sql_out.txt
select emp_name, emp_id from emp where dept='sales';
spool off;
we can see the out on /tmp/sql_out.txt file.
SPOOL command creates a print file of the report.

Q.What are advantages fo Stored Procedures
Extensibility,Modularity, Reusability, Maintainability and one time compilation.

Q.IS Stored Function Is Pre-Compiled as Stored Procedure ? If No Why
stored procedure means the pre-compiled precedure ,which is used for a specific action to be executed more than one times whenever you called from coding in the programe.
stored procedure is an important concept in the application developement in oracle.

Q.Explain the two type of Cursors ?
There are two types of cursors, Implicit Cursor and Explicit Cursor.
PL/SQL uses Implicit Cursors for queries. User defined cursors are called Explicit Cursors. They can be declared and used.

Q.What is Overloading of procedures ?
Overloading of procedure
name of the procedure is
same but the number of parameters should be different.In that case,procedure will be overloaded.
2. if the number of parameters are same in that case,data type should be different.
if the two rules are satisfied in that case procedure will be overloaded.

Q.What is PL/SQL ?
PL/SQL is a procedural language that has both interactive SQL and procedural programming language constructs such as iteration, conditional branching.

Q.What are the PL/SQL Statements used in cursor processing ?
DECLARE CURSOR cursor name, OPEN cursor name, FETCH cursor name INTO or Record types, CLOSE cursor name.

Q.What is Set Transaction?
Set Transaction is to establish properties for the current transaction.

Q.What is Character Functions?
Character Functions are INITCAP, UPPER, LOWER, SUBSTR & LENGTH. Additional functions are GREATEST & LEAST. Group Functions returns results based upon groups of rows rather than one result per row, use group functions. They are AVG, COUNT, MAX, MIN & SUM.

Q.What is an Exception ? What are types of Exception? 
Exception is the error handling part of PL/SQL block. The types are Predefined and user defined. Some of Predefined exceptions are.
CURSOR_ALREADY_OPEN
DUP_VAL_ON_INDEX
NO_DATA_FOUND
TOO_MANY_ROWS
INVALID_CURSOR
INVALID_NUMBER
LOGON_DENIED
NOT_LOGGED_ON
PROGRAM-ERROR
STORAGE_ERROR
TIMEOUT_ON_RESOURCE
VALUE_ERROR
ZERO_DIVIDE
OTHERS.

Q.Is it possible to use Transaction control Statements such a ROLLBACK or COMMIT in Database Trigger? Why?
 
It is not possible. As triggers are defined for each table, if you use COMMIT of ROLLBACK in a trigger, it affects logical transaction processing.
yes WE can use COMMIT and ROLLBACK triggers, but by using PRAGAMA AUTONAMOUS_TRANSATIONS. Now the transation treated as a autonomous tansation.

Q.What is Multiple columns? 
Multiple columns can be returned from a Nested Subquery.

Q.What is Savepoint? 
Savepoint is a point within a particular transaction to which you may rollback without rolling back the entire transaction.