rdbms.pdf plsql database system notes for students to study

PL/SQL Basics
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.
 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.
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.
PL/SQL - Basic Syntax
PL/SQL programs are divided and written in logical blocks of code. Each block consists of three sub-parts
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.

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.
Exception Handling
This section starts with the keyword EXCEPTION. This optional section contains exception(s) that
handle errors in the program.
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 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.
The PL/SQL 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.
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 Numeric Data Types and Subtypes
PL/SQL Character Data Types and Subtypes
PL/SQL Boolean Data Types
PL/SQL Datetime and Interval Types
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]
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;
/
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;
/
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;
/
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

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- Addition, Subtraction, Multiplication, Division
 Relational operators- Less then, Greater Than, etc.
 Comparison operators- Like ,Between, In, IsNull
 Logical operators- AND, OR, NOT
 String operators-
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.
PL/SQL – Loops
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.
DECLARE
i number(1);
j number(1);
BEGIN
<< outer_loop >>
FOR i IN 1..3 LOOP
<< inner_loop >>
FOR j IN 1..3 LOOP
dbms_output.put_line('i is: '|| i || ' and j is: ' || j);
END loop inner_loop;
END loop outer_loop;
END;
/
PL/SQL – Arrays
The 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, however it is often better 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 VARRAY 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.
For example −
TYPE namearray IS VARRAY(5) OF VARCHAR2(10);
Type grades IS VARRAY(5) OF INTEGER;
Example-1
DECLARE
type namesarray IS VARRAY(5) OF VARCHAR2(10);
type grades IS VARRAY(5) OF INTEGER;
names namesarray;
marks grades;
total integer;
BEGIN
names := namesarray('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;
/

Example-2
Elements of a varray could also be a %ROWTYPE of any database table or %TYPE of any database table
field. The following example illustrates the concept.
DECLARE
CURSOR c_customers is
SELECT name FROM customers;
type c_list is varray (6) of customers.name%type;
name_list c_list := c_list();
counter integer :=0;
BEGIN
FOR n IN c_customers LOOP
counter := counter + 1;
name_list.extend;
name_list(counter) := n.name;
dbms_output.put_line('Customer('||counter ||'):'||name_list(counter));
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.
Parts of a PL/SQL Subprogram
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.
Executable Part
This is a mandatory part and contains statements that perform the designated action.

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 PROCEDUREstatement. 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
The procedure can also be called from another PL/SQL block −
BEGIN
greetings;
END;
/

The above call will display −
Hello World
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;
Methods for Passing Parameters
Actual parameters can be passed in three ways −
 Positional notation-
findMin(a, b, c, d);
 Named notation
findMin(x => a, y => b, z => c, m => d);
 Mixed notation
findMin(a, b, c, m => d);
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
CREATE OR REPLACE FUNCTION totalCustomers
RETURN number IS
total number(2) := 0;
BEGIN
SELECT count(*) into total
FROM customers;
RETURN total;
END;
/
Calling a Function
DECLARE
c number(2);
BEGIN
c := totalCustomers();
dbms_output.put_line('Total no. of Customers: ' || c);
END;
/
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;
/
Maximum of (23,45): 45

PL/SQLRecursive 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;
/
Factorial 6 is 720
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 −
%FOUND
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
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
Always returns FALSE for implicit cursors, because Oracle closes the SQL cursor automatically after
executing its associated SQL statement.
%ROWCOUNT
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
he 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;
6 customers selected
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;
1 Ramesh Ahmedabad
2 Khilan Delhi
3 kaushik Kota
4 Chaitali Mumbai
5 Hardik Bhopal
6 Komal MP

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;
/
Customer ID: 5
Customer Name: Hardik
Customer Address: Bhopal
Customer Salary: 9000
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;
/
1 Ramesh
2 Khilan
3 kaushik
4 Chaitali
5 Hardik
6 Komal
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),
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;
book2.title := 'Telecom Billing';
book2.author := 'Zara Ali';
book2.subject := 'Telecom Billing Tutorial';
-- 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;
/
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
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),
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
book1.title := 'C Programming';
book1.author := 'Nuha Ali ';
book1.subject := 'C Programming Tutorial';
book2.title := 'Telecom Billing';
book2.author := 'Zara Ali';
book2.subject := 'Telecom Billing Tutorial';
-- Use procedure to print book info
printbook(book1);
printbook(book2);
END;
/
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 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
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;
/

Trigger created.
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

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