PL/SQL is a combination of SQL along with the procedural features of programming languages.

It was
developed by Oracle Corporation in the early 90's to enhance the capabilities of SQL. PL/SQL is one of
three key programming languages embedded in the Oracle Database, along with SQL itself and Java. This
tutorial will give you great understanding on PL/SQL to proceed with Oracle database and other
advanced RDBMS concepts.

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 certain
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.

Features of PL/SQL
PL/SQL has the following features −

 PL/SQL is tightly integrated with SQL.

 It offers extensive error checking.
 It offers numerous data types.
 It offers a variety of programming structures.
 It supports structured programming through functions and procedures.
 It supports object-oriented programming.
 It supports the development of web applications and server pages.

Advantages of PL/SQL
PL/SQL has the following advantages −

 SQL is the standard database language and PL/SQL is strongly integrated with SQL.
PL/SQL supports both static and dynamic SQL. Static SQL supports DML operations
and transaction control from PL/SQL block. In Dynamic SQL, SQL allows embedding
DDL statements in PL/SQL blocks.
 PL/SQL allows sending an entire block of statements to the database at one time. This
reduces network traffic and provides high performance for the applications.
 PL/SQL gives high productivity to programmers as it can query, transform, and update
data in a database.
 PL/SQL saves time on design and debugging by strong features, such as exception
handling, encapsulation, data hiding, and object-oriented data types.
 Applications written in PL/SQL are fully portable.
  PL/SQL provides high security level.
 PL/SQL provides access to predefined SQL packages.
 PL/SQL provides support for Object-Oriented Programming.
 PL/SQL provides support for developing Web Applications and Server Pages.

 In this chapter, we will discuss the Basic Syntax of PL/SQL which is a block-structured
language; this means that the PL/SQL programs are divided and written in logical blocks
of code. Each block consists of three sub-parts −

S.No Sections & Description

Declarations
1
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.
Executable Commands

2 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.
Exception Handling
3
This section starts with the keyword EXCEPTION. This optional section 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. Following 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 the 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 the SQL prompt, it produces the
following result −
 Hello World

 PL/SQL procedure successfully completed.

 The PL/SQL Identifiers

 PL/SQL identifiers are constants, variables, exceptions, procedures, cursors, and reserved
words. The identifiers consist of a letter optionally followed by more letters, numerals,
dollar signs, underscores, and number signs and should not exceed 30 characters.
 By default, identifiers are not case-sensitive. So you can use integer or INTEGER to
represent a numeric value. You cannot use a reserved keyword as an identifier.

he PL/SQL Comments
Program comments are explanatory statements that can be included in the PL/SQL code that you
write and helps anyone reading its source code. All programming languages allow some form of
comments.

The PL/SQL supports single-line and multi-line comments. All characters available inside any
comment are ignored by the PL/SQL compiler. The PL/SQL single-line comments start with the
delimiter -- (double hyphen) and multi-line comments are enclosed by /* and */.

DECLARE
-- variable declaration
message varchar2(20):= 'Hello, World!';
BEGIN
/*
* PL/SQL executable statement(s)
*/
dbms_output.put_line(message);
END;
/

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

Hello World

PL/SQL procedure successfully completed.

PL/SQL Program Units

A PL/SQL unit is any one of the following −
  PL/SQL block
 Function
 Package
 Package body
 Procedure
 Trigger
 Type
 Type body

PL/SQL - Data Types

The PL/SQL variables, constants and parameters must have a valid data type, which specifies a
storage format, constraints, and a valid range of values. We will focus on the SCALAR and the
LOB data types in this chapter. The other two data types will be covered in other chapters.

S.No Category & Description

Scalar
1
Single values with no internal components, such as a NUMBER, DATE, or BOOLEAN.
Large Object (LOB)
2
Pointers to large objects that are stored separately from other data items, such as text,
graphic images, video clips, and sound waveforms.
Composite
3
Data items that have internal components that can be accessed individually. For example,
collections and records.
Reference
4
Pointers to other data items.

PL/SQL Scalar Data Types and Subtypes

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

S.No Date Type & Description

Numeric
1
Numeric values on which arithmetic operations are performed.
Character
2
Alphanumeric values that represent single characters or strings of characters.
3 Boolean
 Logical values on which logical operations are performed.
Datetime
4
Dates and times.

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

PL/SQL Numeric Data Types and Subtypes

Following table lists out the PL/SQL pre-defined numeric data types and their sub-types −

S.No Data Type & Description

PLS_INTEGER
1
Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
BINARY_INTEGER
2
Signed integer in range -2,147,483,648 through 2,147,483,647, represented in 32 bits
BINARY_FLOAT
3
Single-precision IEEE 754-format floating-point number
BINARY_DOUBLE
4
Double-precision IEEE 754-format floating-point number
NUMBER(prec, scale)
5
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)
6
ANSI specific fixed-point type with maximum precision of 38 decimal digits
DECIMAL(prec, scale)
7
IBM specific fixed-point type with maximum precision of 38 decimal digits
NUMERIC(pre, secale)
8
Floating type with maximum precision of 38 decimal digits
9 DOUBLE PRECISION

ANSI specific floating-point type with maximum precision of 126 binary digits
 (approximately 38 decimal digits)
FLOAT
10
ANSI and IBM specific floating-point type with maximum precision of 126 binary digits
(approximately 38 decimal digits)
INT
11
ANSI specific integer type with maximum precision of 38 decimal digits
INTEGER
12
ANSI and IBM specific integer type with maximum precision of 38 decimal digits
SMALLINT
13
ANSI and IBM specific integer type with maximum precision of 38 decimal digits
REAL
14
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 −

S.No Data Type & Description

CHAR
1
Fixed-length character string with maximum size of 32,767 bytes
VARCHAR2
2
Variable-length character string with maximum size of 32,767 bytes
 RAW
3
Variable-length binary or byte string with maximum size of 32,767 bytes, not interpreted
by PL/SQL
NCHAR
4
Fixed-length national character string with maximum size of 32,767 bytes
NVARCHAR2
5
Variable-length national character string with maximum size of 32,767 bytes
LONG
6
Variable-length character string with maximum size of 32,760 bytes
LONG RAW
7
Variable-length binary or byte string with maximum size of 32,760 bytes, not interpreted
by PL/SQL
ROWID
8
Physical row identifier, the address of a row in an ordinary table
UROWID
9
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 is used 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
01 to 31 (limited by the values of MONTH
DAY and YEAR, according to the rules of the Any nonzero integer
calendar for the locale)
HOUR 00 to 23 0 to 23
MINUTE 00 to 59 0 to 59
0 to 59.9(n), where 9(n)
00 to 59.9(n), where 9(n) is the precision of is the precision of
SECOND
time fractional seconds interval fractional
seconds
-12 to 14 (range accommodates daylight
TIMEZONE_HOUR Not applicable
savings time changes)
TIMEZONE_MINUTE 00 to 59 Not applicable
Found in the dynamic performance view
TIMEZONE_REGION Not applicable
V$TIMEZONE_NAMES
Found in the dynamic performance view
TIMEZONE_ABBR Not applicable
V$TIMEZONE_NAMES

PL/SQL Large Object (LOB) Data Types

Large Object (LOB) data types refer to large 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

Used to store large binary objects in System-dependent. Cannot
BFILE
operating system files outside the database. exceed 4 gigabytes (GB).
Used to store large binary objects in the
BLOB 8 to 128 terabytes (TB)
database.
Used to store large blocks of character data
CLOB 8 to 128 TB
in the database.
Used to store large blocks of NCHAR data
NCLOB 8 to 128 TB
in the database.
PL/SQL - Variables
A variable is nothing but a name given to a storage area that our programs can manipulate. Each
variable in PL/SQL has a specific data type, which determines the size and the layout of the
variable's memory; the range of values that can be stored within that memory and the set of
operations that can be applied to the variable.

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.

PL/SQL programming language allows to define various types of variables, such as date time
data types, records, collections, etc. which we will cover in subsequent chapters. For this chapter,
let us study only basic variable types.

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 the 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, sometimes programs

would produce unexpected results. 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.

(For SQL statements, please refer to the SQL tutorial)

CREATE TABLE CUSTOMERS(

ID INT NOT NULL,
NAME VARCHAR (20) NOT NULL,
AGE INT NOT NULL,
ADDRESS CHAR (25),
SALARY DECIMAL (18, 2),
PRIMARY KEY (ID)
);

Table Created

Let us now insert some values in the table −

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (1, 'Ramesh', 32, 'Ahmedabad', 2000.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (2, 'Khilan', 25, 'Delhi', 1500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (3, 'kaushik', 23, 'Kota', 2000.00 );
INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, 'Chaitali', 25, 'Mumbai', 6500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (5, 'Hardik', 27, 'Bhopal', 8500.00 );

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (6, 'Komal', 22, 'MP', 4500.00 );

The following program assigns values from the above table to PL/SQL variables using the
SELECT INTO clause of SQL −

DECLARE
c_id customers.id%type := 1;
c_name customerS.No.ame%type;
c_addr customers.address%type;
c_sal customers.salary%type;
BEGIN
SELECT name, address, salary INTO c_name, c_addr, c_sal
FROM customers
WHERE id = c_id;
dbms_output.put_line
('Customer ' ||c_name || ' from ' || c_addr || ' earns ' || c_sal);
END;
/

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

Customer Ramesh from Ahmedabad earns 2000

PL/SQL procedure completed successfully

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 the 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.

S.No Literal Type & Example

Numeric Literals

050 78 -14 0 +32767

1
6.6667 0.0 -12.0 3.14159 +7800.00

6E5 1.0E-8 3.14159e0 -1E38 -9.5e-3

2 Character Literals
 'A' '%' '9' ' ' 'z' '('
String Literals

'Hello, world!'
3
'Tutorials Point'

'19-NOV-12'
BOOLEAN Literals
4
TRUE, FALSE, and NULL.
Date and Time Literals
5 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 in the following program −

DECLARE
message varchar2(30):= 'That''s tutorialspoint.com!';
BEGIN
dbms_output.put_line(message);
END;
/

When the above code is executed at the 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 types of
operators −

 Arithmetic operators
 Relational operators
 Comparison operators
 Logical operators
 String operators
Here, we will understand the arithmetic, relational, comparison and logical operators one by one.
The String operators will be discussed in a later chapter − PL/SQL - Strings.

Arithmetic Operators
Following table shows all the arithmetic operators supported by PL/SQL. Let us 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. Let us 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 (A = B) is not
=
becomes true. true.

!=
Checks if the values of two operands are equal or not, if values are not equal
<> (A != B) is true.
then condition becomes true.

~=
Checks if the value of left operand is greater than the value of right operand, (A > B) is not
>
if yes then condition becomes true. true.

Checks if the value of left operand is less than the value of right operand, if
< (A < B) is true.
yes then condition becomes true.
 Checks if the value of left operand is greater than or equal to the value of (A >= B) is not
>=
right operand, if yes then condition becomes true. true.

Checks if the value of left operand is less than or equal to the value of right
<= (A <= B) is true
operand, if yes then condition becomes 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

The LIKE operator compares a character, string, or If 'Zara Ali' like 'Z% A_i' returns a
LIKE CLOB value to a pattern and returns TRUE if the Boolean true, whereas, 'Nuha Ali' like 'Z
value matches the pattern and FALSE if it does not. % A_i' returns a Boolean false.

If x = 10 then, x between 5 and 20

The BETWEEN operator tests whether a value lies in
returns true, x between 5 and 10
BETWEEN a specified range. x BETWEEN a AND b means that x
returns true, but x between 11 and 20
>= a and x <= b.
returns false.

If x = 'm' then, x in ('a', 'b', 'c') returns

The IN operator tests set membership. x IN (set)
IN Boolean false but x in ('m', 'n', 'o')
means that x is equal to any member of set.
returns Boolean true.

The IS NULL operator returns the BOOLEAN value

TRUE if its operand is NULL or FALSE if it is not NULL. If x = 'm', then 'x is null' returns Boolean
IS NULL
Comparisons involving NULL values always yield false.
NULL.

Logical Operators
Following table shows the Logical operators supported by PL/SQL. All these operators work on
Boolean operands and produce Boolean results. Let us assume variable A holds true and
variable B holds false, then −

Operator Description Examples

and Called the logical AND operator. If both the operands are true then condition (A and B) is
 becomes true. false.

Called the logical OR Operator. If any of the two operands is true then
or (A or B) is true.
condition becomes true.

Called the logical NOT Operator. Used to reverse the logical state of its not (A and B) is
not
operand. If a condition is true then Logical NOT operator will make it false. 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.

The precedence of operators goes as follows: =, <, >, <=, >=, <>, !=, ~=, ^=, IS NULL, LIKE,
BETWEEN, IN.

Show Examples

Operator Operation

** exponentiation

+, - identity, negation

*, / multiplication, division

+, -, || addition, subtraction, concatenation

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.

Following is the general form of a typical conditional (i.e., decision making) structure found in
most of the programming languages −

PL/SQL programming language provides following types of decision-making statements. Click

the following links to check their detail.

S.No Statement & Description

1 IF - THEN statement

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.

DECLARE
a number(2) := 10;
BEGIN
a:= 10;
-- check the boolean condition using if statement
 IF( a < 20 ) THEN
-- if condition is true then print the following
dbms_output.put_line('a is less than 20 ' );
END IF;
dbms_output.put_line('value of a is : ' || a);
END;
/

IF-THEN-ELSE statement

IF statement adds the keyword ELSE followed by an alternative sequence of statement.

If the condition is false or NULL, then only the alternative sequence of statements get
executed. It ensures that either of the sequence of statements is executed.

DECLARE
a number(3) := 100;
BEGIN
-- check the boolean condition using if statement
2 IF( a < 20 ) THEN
-- if condition is true then print the following
dbms_output.put_line('a is less than 20 ' );
ELSE
dbms_output.put_line('a is not less than 20 ' );
END IF;
dbms_output.put_line('value of a is : ' || a);
END;
/

IF-THEN-ELSIF statement

It allows you to choose between several alternatives.

DECLARE
a number(3) := 100;
BEGIN
IF ( a = 10 ) THEN
dbms_output.put_line('Value of a is 10' );
ELSIF ( a = 20 ) THEN
dbms_output.put_line('Value of a is 20' );
ELSIF ( a = 30 ) THEN
dbms_output.put_line('Value of a is 30' );
ELSE
dbms_output.put_line('None of the values is matching');
END IF;
dbms_output.put_line('Exact value of a is: '|| a );
END;
/
 Case statement

Like the IF statement, the CASE statement selects one sequence of statements to execute

DECLARE
grade char(1) := 'A';
BEGIN
CASE grade
when 'A' then dbms_output.put_line('Excellent');
when 'B' then dbms_output.put_line('Very good');
when 'C' then dbms_output.put_line('Well done');
when 'D' then dbms_output.put_line('You passed');
when 'F' then dbms_output.put_line('Better try again');
else dbms_output.put_line('No such grade');
END CASE;
END;
/

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.

nested IF-THEN-ELSE
5
You can use one IF-THEN or IF-THEN-ELSIF statement inside another IF-THEN or
IF-THEN-ELSIF statement(s).
DECLARE
a number(3) := 100;
b number(3) := 200;
BEGIN
-- check the boolean condition
IF( a = 100 ) THEN
-- if condition is true then check the following
IF( b = 200 ) THEN
-- if condition is true then print the following
dbms_output.put_line('Value of a is 100 and b is 200' );
END IF;
END IF;
dbms_output.put_line('Exact value of a is : ' || a );
dbms_output.put_line('Exact value of b is : ' || b );
END;
/
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 −

PL/SQL provides the following types of loop to handle the looping requirements. Click the
following links to check their detail.

S.No Loop Type & Description

1 PL/SQL Basic LOOP

In this loop structure, sequence of statements is enclosed between the LOOP and the END
LOOP statements. At each iteration, the sequence of statements is executed and then
control resumes at the top of the loop.

DECLARE
x number := 10;
BEGIN
LOOP
dbms_output.put_line(x);
 x := x + 10;
IF x > 50 THEN
exit;
END IF;
END LOOP;
-- after exit, control resumes here
dbms_output.put_line('After Exit x is: ' || x);
END;
/

Exit When
DECLARE
x number := 10;
BEGIN
LOOP
dbms_output.put_line(x);
x := x + 10;
exit WHEN x > 50;
END LOOP;
-- after exit, control resumes here
dbms_output.put_line('After Exit x is: ' || x);
END;
/

PL/SQL WHILE LOOP

Repeats a statement or group of statements while a given condition is true. It tests the
condition before executing the loop body.

DECLARE
a number(2) := 10;
2 BEGIN
WHILE a < 20 LOOP
dbms_output.put_line('value of a: ' || a);
a := a + 1;
END LOOP;
END;
/

3 PL/SQL FOR LOOP

Execute a sequence of statements multiple times and abbreviates the code that manages
the loop variable.

DECLARE
a number(2);
BEGIN
FOR a in 10 .. 20 LOOP
dbms_output.put_line('value of a: ' || a);
END LOOP;
END;
 /

Reverse FOR LOOP Statement

DECLARE
a number(2) ;
BEGIN
FOR a IN REVERSE 10 .. 20 LOOP
dbms_output.put_line('value of a: ' || a);
END LOOP;
END;
/

Nested loops in PL/SQL

You can use one or more loop inside any another basic loop, while, or for loop.

DECLARE
i number(3);
j number(3);
BEGIN
i := 2;
LOOP
j:= 2;
LOOP
4 exit WHEN ((mod(i, j) = 0) or (j = i));
j := j +1;
END LOOP;
IF (j = i ) THEN
dbms_output.put_line(i || ' is prime');
END IF;
i := i + 1;
exit WHEN i = 50;
END LOOP;
END;
/

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 the schema level

  Inside a package
 Inside a PL/SQL block

At the schema level, subprogram is a standalone subprogram. It is created with the CREATE
PROCEDURE or the 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. We will discuss
PL/SQL function in the next chapter.

Parts of a PL/SQL Subprogram

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

S.No Parts & Description

Declarative Part

1 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.
Executable Part
2
This is a mandatory part and contains statements that perform the designated action.
Exception-handling
3
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 the modification of an existing procedure.
 The optional parameter list contains name, mode and types of the parameters. IN
represents the value that will be passed from outside and OUT represents the parameter
that 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.

Example

The following example creates a simple procedure that displays the string 'Hello World!' on the
screen when executed.

CREATE OR REPLACE PROCEDURE greetings

AS
BEGIN
dbms_output.put_line('Hello World!');
END;
/

When the above code is executed using the SQL prompt, it will produce the following result −

Procedure created.

Executing a Standalone Procedure

A standalone procedure can be called in two ways −

 Using the EXECUTE keyword

 Calling the name of the procedure from a PL/SQL block

The above procedure named 'greetings' can be called with the EXECUTE keyword as −

EXECUTE greetings;

The above call will display −

Hello World

PL/SQL procedure successfully completed.

The procedure can also be called from another PL/SQL block −

BEGIN
greetings;
END;
/

The above call will display −

Hello World

PL/SQL procedure successfully completed.

Deleting a Standalone Procedure

A standalone procedure is deleted with the DROP PROCEDURE statement. Syntax for deleting
a procedure is −

DROP PROCEDURE procedure-name;

You can drop the greetings procedure by using the following statement −

DROP PROCEDURE greetings;

Parameter Modes in PL/SQL Subprograms

The following table lists out the parameter modes in PL/SQL subprograms −

S.No Parameter Mode & Description

IN

An IN parameter lets you pass a value to the subprogram. It is a read-only parameter.

1 Inside the subprogram, an IN parameter acts like a constant. It cannot be assigned a value.
You can pass a constant, literal, initialized variable, or expression as an IN parameter. You
can also initialize it to a default value; however, in that case, it is omitted from the
subprogram call. It is the default mode of parameter passing. Parameters are passed
by reference.
OUT
2 An OUT parameter returns a value to the calling program. Inside the subprogram, an OUT
parameter acts like a variable. You can change its value and reference the value after
assigning it. The actual parameter must be variable and it is passed by value.
 IN OUT

An IN OUT parameter passes an initial value to a subprogram and returns an updated

3 value to the caller. It can be assigned a value and the value can be read.

The actual parameter corresponding to an IN OUT formal parameter must be a variable,

not a constant or an expression. Formal parameter must be assigned a value. Actual
parameter is passed by value.
IN & OUT Mode Example 1

This program finds the minimum of two values. Here, the procedure takes two numbers using the
IN mode and returns their minimum using the OUT parameters.

DECLARE
a number;
b number;
c number;
PROCEDURE findMin(x IN number, y IN number, z OUT number) IS
BEGIN
IF x < y THEN
z:= x;
ELSE
z:= y;
END IF;
END;
BEGIN
a:= 23;
b:= 45;
findMin(a, b, c);
dbms_output.put_line(' Minimum of (23, 45) : ' || c);
END;
/

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

Minimum of (23, 45) : 23

PL/SQL procedure successfully completed.

IN & OUT Mode Example 2

This procedure computes the square of value of a passed value. This example shows how we can
use the same parameter to accept a value and then return another result.

DECLARE
a number;
PROCEDURE squareNum(x IN OUT number) IS
BEGIN
x := x * x;
END;
BEGIN
a:= 23;
 squareNum(a);
dbms_output.put_line(' Square of (23): ' || a);
END;
/

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

Square of (23): 529

PL/SQL procedure successfully completed.

PL/SQL - Functions
A function is same as a procedure except that it returns a value. Therefore, all the discussions of
the previous chapter are true for functions too.

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

Example

The following example illustrates how to create and call a standalone function. This function
returns the total number of CUSTOMERS in the customers table.

We will use the CUSTOMERS table, which we had created in the PL/SQL Variables chapter −
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 |
+----+----------+-----+-----------+----------+
CREATE OR REPLACE FUNCTION totalCustomers
RETURN number IS
total number(2) := 0;
BEGIN
SELECT count(*) into total
FROM customers;

RETURN total;
END;
/

When the above code is executed using the SQL prompt, it will produce the following result −

Function created.

Calling a Function
While creating a function, you give a definition of what the function has to do. To use a function,
you will have to call that function to perform the defined task. When a program calls a function,
the program control is transferred to the called function.

A called function performs the defined task and when its return statement is executed or when
the last end statement is reached, it returns the program control back to the main program.

To call a function, you simply need to pass the required parameters along with the function name
and if the function returns a value, then you can store the returned value. Following program
calls the function totalCustomers from an anonymous block −

DECLARE
c number(2);
BEGIN
c := totalCustomers();
dbms_output.put_line('Total no. of Customers: ' || c);
END;
/

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

Total no. of Customers: 6

PL/SQL procedure successfully completed.
Example

The following example demonstrates Declaring, Defining, and Invoking a Simple PL/SQL
Function that computes and returns the maximum of two values.

DECLARE
a number;
b number;
c number;
FUNCTION findMax(x IN number, y IN number)
RETURN number
IS
z number;
BEGIN
IF x > y THEN
z:= x;
ELSE
Z:= y;
END IF;
RETURN z;
END;
BEGIN
a:= 23;
b:= 45;
c := findMax(a, b);
dbms_output.put_line(' Maximum of (23,45): ' || c);
END;
/

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

Maximum of (23,45): 45

PL/SQL procedure successfully completed.

PL/SQL Recursive Functions

We have seen that a program or subprogram may call another subprogram. When a subprogram
calls itself, it is referred to as a recursive call and the process is known as recursion.

To illustrate the concept, let us calculate the factorial of a number. Factorial of a number n is
defined as −

n! = n*(n-1)!
= n*(n-1)*(n-2)!
...
= n*(n-1)*(n-2)*(n-3)... 1

The following program calculates the factorial of a given number by calling itself recursively −
DECLARE
num number;
factorial number;

FUNCTION fact(x number)

RETURN number
IS
f number;
BEGIN
IF x=0 THEN
f := 1;
ELSE
f := x * fact(x-1);
END IF;
RETURN f;
END;

BEGIN
num:= 6;
factorial := fact(num);
dbms_output.put_line(' Factorial '|| num || ' is ' || factorial);
END;
/

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

Factorial 6 is 720

PL/SQL procedure successfully completed.

PL/SQL - Cursors
Oracle creates a memory area, known as the context area, for processing an SQL statement,
which contains all the information needed for processing the statement; for example, the 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 attributes such as %FOUND, %ISOPEN, %NOTFOUND, and %ROWCOUNT. The
SQL cursor has additional attributes, %BULK_ROWCOUNT and %BULK_EXCEPTIONS,
designed for use with the FORALL statement. The following table provides the description of
the most used attributes −

S.No Attribute & Description

%FOUND
1
Returns TRUE if an INSERT, UPDATE, or DELETE statement affected one or more rows
or a SELECT INTO statement returned one or more rows. Otherwise, it returns FALSE.
%NOTFOUND
2 The logical opposite of %FOUND. It returns TRUE if an INSERT, UPDATE, or DELETE
statement affected no rows, or a SELECT INTO statement returned no rows. Otherwise, it
returns FALSE.
%ISOPEN
3
Always returns FALSE for implicit cursors, because Oracle closes the SQL cursor
automatically after executing its associated SQL statement.
%ROWCOUNT
4
Returns the number of rows affected by an INSERT, UPDATE, or DELETE statement, or
returned by a SELECT INTO statement.

Any SQL cursor attribute will be accessed as sql%attribute_name as shown below in the
example.

Example

We will be using the CUSTOMERS table we had created and used in the previous chapters.

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 will update the table and increase the salary of each customer by 500 and
use the SQL%ROWCOUNT attribute to determine the number of rows affected −

DECLARE
total_rows number(2);
BEGIN
UPDATE customers
SET salary = salary + 500;
IF sql%notfound THEN
dbms_output.put_line('no customers selected');
ELSIF sql%found THEN
total_rows := sql%rowcount;
dbms_output.put_line( total_rows || ' customers selected ');
END IF;
END;
/

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

6 customers selected

PL/SQL procedure successfully completed.

If you check the records in customers table, you will find that the rows have been updated −

Select * from customers;

+----+----------+-----+-----------+----------+
| ID | NAME | AGE | ADDRESS | SALARY |
+----+----------+-----+-----------+----------+
| 1 | Ramesh | 32 | Ahmedabad | 2500.00 |
| 2 | Khilan | 25 | Delhi | 2000.00 |
| 3 | kaushik | 23 | Kota | 2500.00 |
| 4 | Chaitali | 25 | Mumbai | 7000.00 |
| 5 | Hardik | 27 | Bhopal | 9000.00 |
| 6 | Komal | 22 | MP | 5000.00 |
+----+----------+-----+-----------+----------+

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 includes the following steps −

 Declaring the cursor for initializing the memory

 Opening the cursor for allocating the memory
 Fetching the cursor for retrieving the data
 Closing the cursor to release the 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 the memory for the cursor and makes it ready for fetching the rows
returned by the SQL statement into it. For example, we will open the 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 the above-
opened cursor as follows −

CLOSE c_customers;
Example

Following is a complete example to illustrate the concepts of explicit cursors &minua;

DECLARE
c_id customers.id%type;
 c_name customerS.No.ame%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;
EXIT WHEN c_customers%notfound;
dbms_output.put_line(c_id || ' ' || c_name || ' ' || c_addr);
END LOOP;
CLOSE c_customers;
END;
/

When the above code is executed at the 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 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.

For example, you want to keep track of your books in a library. You might want to track the
following attributes about each book, such as Title, Author, Subject, Book ID. A record
containing a field for each of these items allows treating a BOOK as a logical unit and allows
you to organize and represent its information in a better way.

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 cursorbased
records.

The following example illustrates 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 the 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 illustrates 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 the 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 the different record
structures. These 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;

The Book record is declared in the following way −

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
an example to explain the 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 the 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.

Records as Subprogram Parameters

You can pass a record as a subprogram parameter just as you pass any other variable. You can
also access the record fields in the same way as you accessed in the above example −

DECLARE
type books is record
(title varchar(50),
author varchar(50),
subject varchar(100),
book_id number);
book1 books;
book2 books;
PROCEDURE printbook (book books) IS
BEGIN
dbms_output.put_line ('Book title : ' || book.title);
dbms_output.put_line('Book author : ' || book.author);
dbms_output.put_line( 'Book subject : ' || book.subject);
dbms_output.put_line( 'Book book_id : ' || book.book_id);
END;
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;

-- Use procedure to print book info

printbook(book1);
printbook(book2);
END;
/

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

Book title : C Programming

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

PL/SQL procedure successfully completed.

Trigger

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

Triggers can be written for the following purposes −

 Generating some derived column values automatically

 Enforcing referential integrity
 Event logging and storing information on table access
 Auditing
 Synchronous replication of tables
 Imposing security authorizations
 Preventing invalid transactions

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 will 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 will 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, such as INSERT, UPDATE, and DELETE.
 [FOR EACH ROW] − This specifies a row-level trigger, i.e., the trigger will 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 we had created and used in the previous
chapters −

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 the SQL prompt, it produces the following result −

Trigger created.

The following points need to be considered here −

 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.
 The 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 the DELETE operation on the table.
Triggering a Trigger
Let us perform some DML operations on the CUSTOMERS table. Here is one INSERT
statement, which will create a new record in the table −

INSERT INTO CUSTOMERS (ID,NAME,AGE,ADDRESS,SALARY)

VALUES (7, 'Kriti', 22, 'HP', 7500.00 );

When a record is created in the CUSTOMERS table, the above create trigger,
display_salary_changes will be fired and it will display the following result −

Old salary:
New salary: 7500
Salary difference:

Because this is a new record, old salary is not available and the above result comes as null. Let
us now perform one more DML operation on the CUSTOMERS table. The UPDATE statement
will update an existing record in the table −

UPDATE customers
SET salary = salary + 500
WHERE id = 2;

When a record is updated in the CUSTOMERS table, the above create trigger,
display_salary_changes will be fired and it will display the following result −

Old salary: 1500

New salary: 2000
Salary difference: 500