CH-4:- PL/SQL

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ORACLE MATERIAL (B.CA. & B.SC.(I.T.) SEM-3)

CH-4:- PL/SQL

Difference between SQL and PL/SQL. DETAILING:-

SQL PL/SQL

SQL statements are passed to the Oracle Engine one at a time. Each time an SQL statement is executed, a call is made to the engine’s resources, which increases network traffic.

PL/SQL sends an entire block of SQL statements to the Oracle engine all in one go. Since the Oracle engine got the SQL statements as a single block, it processes this code much faster than one sentence at a time.

SQL does not have any procedural capabilities like Conditional checking using conditional statement, looping and branching, declaration and use of variable to store intermediate result.

PL/SQL is development tool that supports facilities of conditional checking, branching and looping, declaration and use of variable to store intermediate result.

SQL has no facility for programmed handling of errors and so if an error occurs, the Oracle engine displays its own error messages.

PL/SQL also permits dealing with errors as required, and facilitates displaying user-friendly messages, when errors are encountered.

In SQL it is not possible to perform calculations without the use of the Oracle Engine.

PL/SQL facilitates all sorts of calculations can be done quickly and efficiently without the use of the Oracle engine.



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ONE WORD QUESTION AND ANSWER SR.NO QUESTION ANSWER

1. FULL FORM OF SQL STRUCTURE QUERY LANGUAGE

2 SQL IS LANGUAGE? YES

3 PL/SQL MEANS PROCEDURAL STRUCTURE QUERY LANGUAGE.

4 WHY WE CAN USE PL/SQL? IN PL SQL WE CAN USE BRANCHING STATEMENT SO WE CAN USE THIS.

EXPLAIN PL/SQL BLOCK STRUCTURE. DETAILING:-



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A single PL/SQL code block consists of a set of SQL statements, clubbed together, and passed to the Oracle engine entirely.

A PL/SQL block has a definite structure, which can be divided into sections.

The sections of PL/SQL block are:

The Declare section.

The Begin Section.

The Exception section is optional.

The end section.

The Declare Section

PL/SQL block start with a declaration section, in which, memory variables and other Oracle objects can be declared and initialized.

The Begin Section

It consists of a set of SQL and PL/SQL statements.

Data manipulation statements, retrieval of data using SELECT, conditional statements, looping and branching statements are specified in this section.

The Exception Section

This section deals with handling of errors that arise during execution of the data manipulation statements and also user can generate its own user-defined error message.

The End Section

Declarations of memory variables, constants, cursors, etc. in PL/SQL

SQL executable statements PL/SQL executable statements

SQL or PL/SQL code to handle errors that may arise during the execution of the code block between BEGIN and EXCEPTION section

DECLARE

BEGIN

EXCEPTION



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1. HOW MANY PART OF PL/SQL STRUCTURE

4

2 DECLARE MEANS___ DELCARE VARIABLE

3 BEGIN MEANS BODY

4 EXCEPTION IS OPTIONAL? YES

5 END MEANS PROGRAM IS OVER.

EXPLAIN DIFFERENTS TYPES OF LOOP IN PL/SQL. DETAILING:

Iterative control indicates the ability to repeat sections of a code block.

A loop marks a sequence of statements that has to be repeated.

The keyword loop has to be placed before the first statement in the sequence of statements to be repeated, while the keyword end loop is placed immediately after the last statement in the sequence.

PL/SQL supports the following structures for iterative control:

Simple Loop

In simple loop, the keyword loop should be placed before the first statement in the sequence and the keyword end loop should be written at the end of the sequence to end the loop.

Syntax:

Loop Sequence of statements;

End loop;



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The WHILE loop

declare num number := 0; begin loop num:=num + 2; exit when num > 10; end loop;

dbms_output.put_line(‘Loop exited when the value of num has reached’ || to_char(i));

end;

Syntax: WHILE condition LOOP Action; END LOOP;

declare PI number (4, 2):= 3.14; radius number(5); area number(14,2); begin radius := 3; while radius <= 7 loop area := PI * power(radius,2); insert into areas values(radius, area); radius := radius + 1; end loop;



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The FOR Loop

Note: The variable in the FOR loop need not be declared. Also the increment value cannot be specified. By default the for loop variable is always incremented by 1.

Syntax: FOR variable IN [REVERSE] start..end LOOP

Action; END LOOP;

Example: declare strval varchar(10); str_length number(2); reverse_str varchar(10); begin strval:=’&strval’; str_length := length(strval); for i in reverse 1..str_length loop reverse_str := reverse_str || substr(strval,i,1); end loop; dbms_output.put_line(‘Original String is : ‘ || strval); dbms_output.put_line(‘Reverse String is : ‘ || reverse_str); end;



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1. LOOP IS ALSO CALLED _____ ITERATIVE CONTROL STATEMENT

2 WHILE IS ENTERY CONTROL? YES

3 WHICH ONE IS EASY LOOP? FOR

EXPLAIN %TYPE AND %ROWTYPE WITH EXAMPLE. DETAILING:



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%TYPE

PL/SQL uses the %TYPE attribute to declare variables based on definitions of columns in a table so user doesn’t need to remember data type and size of column of table.

If a column’s attributes change, the variable’s attributes will change as well.

This provides for data independence, reduces maintenance costs, and allows program to adapt to changes made to the table.

Syntax:

Tablename.columnname%TYPE;

Example:

declare /*data type of mempno and msal is similar to the data type and size of empno and salary column of emp table.*/ mempno emp.empno%TYPE; msal emp.sal%TYPE; incre_amt number(4); finalsal number(10,2); begin mempno:=&mempno; incre_amt:=&incre_amt; select sal into msal from emp where empno=mempno; finalsal:=msal+incre_amt; update emp set sal=finalsal where empno=mempno; insert into oldsal values(mempno,msal,sysdate); end;



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%ROWTYPE

PL/SQL uses the %ROWTYPE attribute to declare variables based on definitions of entire column in a table so user doesn’t need to remember data type and size of columns of table.

If a column’s attributes change, the variable’s attributes will change as well.

This provides for data independence, reduces maintenance costs, and allows program to adapt to changes made to the table.


1. TYPE AND ROW TYPE ARE ____

ATTRIBUTE.

2 TYPE MEANS ONE COLUMN

3 ROW TYPES MEANS ALL COLUMN

WHAT IS CURSOR? DETAILING:-

The Oracle Engine uses a work area for its internal processing in order to execute an SQL statement.

Syntax: tablename%ROWTYPE;



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This work area is called a Cursor. A cursor is opened at the client end.

The data is stored in the cursor is called the Active Data Set.

The size of the cursor in memory is the size required to hold the number of rows in the Active Data Set. Example:

When a user fires a select statement as: SELECT empno, ename, sal FROM emp WHERE deptno=10;

CURSOR

Types of Cursors Cursors are classified into two types.

1. Implicit Cursor 2. Explicit Cursor

A cursor that is created, opened and managed by Oracle Engine for its

internal processing is known as Implicit Cursor. A cursor that is created, opened and managed through PL/SQL block by the

user is known as Explicit Cursor.

Cursor Attributes:

Cursor Attributes are a set of four system variables, which keep track of the Current status of a cursor.

Both Implicit and Explicit cursors have four attributes.

SERVER

Active Data Set

E1 Ivan 8500

E4 Peter 5700

E5 Robert 9000

E8 Julie 6500



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They are described below:

Attribute Name Description

%ISOPEN Returns TRUE if cursor is open, FALSE otherwise.

%FOUND Returns TRUE if record was fetched successfully, FALSE otherwise.

%NOTFOUND Returns TRUE if record was not fetched successfully, FALSE otherwise.

%ROWCOUNT Returns number of records processed from the cursor.


1. CURSOR MEANS______ WORK AREA

2 IMPLICIT MEANS ORALCE ENGINE

3 EXPLICIT USER

4 HOW MANY TYPES OF ATTRIBUTE ARE IN CURSOR?

4

5 ADT MEANS ACTIVE DATA SET.

EXPLAIN IMPICIT CURSOR WITH EXAMPLE. DETAILING:- Implicit Cursor

A cursor that is created, opened and managed by Oracle Engine for its internal processing is known as Implicit Cursor.

Since the implicit cursor is opened and managed by the Oracle engine internally, the function of reserving an area in memory, filling this area with appropriate data,



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processing the data in the memory area, releasing the memory area when the processing is completed, is taken care of by the Oracle engine.

The name of implicit cursor is always SQL. The implicit cursor has following attribute.

Attribute Name Description

%ISOPEN Returns TRUE if cursor is open, FALSE otherwise.

%FOUND Returns TRUE if record was fetched successfully, FALSE otherwise.

%NOTFOUND Returns TRUE if record was not fetched successfully, FALSE otherwise.

%ROWCOUNT Returns number of records processed from the cursor.


1. IMPLICIT MEANS______ ORALCE ENGINE

2 NAME OF IMPLICIT CURSOR SQL

3 HOW MANY ATTRIBUTE ? 4

begin update emp set sal=sal+(sal*0.15) where empno = &mempno;

if sql%found then dbms_output.put_line('Employee exists…Increment done successfully');

end if; if sql%notfound then dbms_output.put_line('Employee does not exist…Try another number'); end if; end;



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EXPLAIN EXPLICIT CURSOR WITH EXAMPLE.

DETAILING:

When individual records in a table have to be processed inside a PL/SQL code block, a cursor is used. This cursor will be declared and mapped to a SQL query in the Declare Section of the PL/SQL block and used within its Executable Section.

A cursor thus created and used is known as Explicit Cursor. The steps involved in using an explicit cursor and manipulating data in its active

set are:

Declare a cursor mapped to a SQL select statement that retrieves data for processing.

Open the cursor. Fetch data from the cursor one row at a time into memory variables. Process the data held in the memory variables as required using a loop. Exit from the loop after processing is complete. Close the cursor.

Cursor Declaration

A cursor is defined in the declarative part of a PL/SQL block. Naming the cursor and mapping it to a SELECT query is done at this

stage. When a cursor is declared, the Oracle engine is informed that a cursor

of the said name needs to be opened. The declaration is only information.

There is no memory allocation at this point in time.

The Functionality of Open, Fetch and Close Commands

Syntax:

CURSOR CursorName IS SELECT statement;



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Initialization and Opening of a cursor takes place via the Open statement. Open Statement will:

Executes a query associated with the cursor. Creates the Active Data Set that contains all rows, which meet the query search

criteria Sets the row pointer in the Active Data Set to the first record.

Fetching Data from Cursor

A fetch statement then moves the data held in the Active Data Set into memory variables.

Data held in the memory variables can be processed as desired. The fetch statement is placed inside a Loop…End Loop construct, which causes the

data to be fetched into the memory variables and processed until all the rows in the Active Data Set are processed.

The fetch loop then exits.

Closing a Cursor The Close Statement will release the memory occupied by the cursor and its Data

Set both on the Client and on the Server.

Syntax: Open <cursorname>;

Syntax: FETCH CursorName INTO Variable1, Variable2,…;

Syntax: CLOSE <Cursor Name>;

declare /*data type of mempno,mdept and msal is similar to the data type and size of empno, dept and salary column of emp table.*/ /*Defining Cursor*/ cursor c_emp is select empno,sal from emp where dept=’HR’; mempno emp.empno%type; msal emp.sal%type; incre_amt number(4); finalsal emp.sal%type;



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1. EXPLICIT MEANS______ USER

2 WHO WILL CREATE THIS CRSOR

USER

3 CURSOR IS INDEPENDENT OBJECT?

NO

4 IN CURSOR WE CAN USE TYPE AND ROW TYPE?

YES



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WHAT ARE FUNCTION AND PROCEDURE?

DETAILING: A Procedure or Function is a logically grouped set of SQL and PL/SQL statements

that perform a specific task. A stored procedure or function is a named PL/SQL code block that has been

compiled and stored in one of the Oracle engine's system tables.

Procedures and Functions are made up of:

A declarative part

An executable part

An optional exception-handling part

Declarative Part

The declarative part may contain the declarations of cursors, constants, variables, exceptions and subprograms. These objects are local to the procedure or function.

Executable Part

The executable part is a PL/SQL block consisting of SQL and PL/SQL statements that assign values, control execution and manipulate data.

The data that is to be returned back to the calling environment is also returned from here. The variables declared are put to use within this block.

Exception Handling Part

This part contains code that deals with exceptions that may be raised during the execution of code in the executable part.

An Oracle exception handler can be redirected to the exception handling section of the procedure or function where the procedure or function determines the actual action that must be carried out by Oracle's exception handler.

Procedures and Functions are stored in the Oracle database. Before a procedure or function is stored, the Oracle engine parses and compiles the procedure or function.



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The Oracle engine while creating a procedure performs the following steps

automatically:

Compiles the procedure or function

Stores the procedure or function in the database

The status of a procedure or function is shown by the use of a select statement as follows:

ADVANTAGES OF USING A PROCEDURE OR FUNCTION 1. Security 2. Performance 3. Memory Allocation 4. Productivity 5. Integrity


1. PROCEDURE AND FUNCTION MEANS

SPECIAL SPACE THAT WORK ON SPECIAL PROGRAM

2 PROCEDURE AND FUNCTION ARE STORE IN_______

SYSTEM TABLE

3 PROCEDURE AND FUCNTION COMPILE AUTOMATICALLY

YES

Note: The compilation process does not display the errors. These errors can be viewed by giving “show err” command at sql prompt or by using “SELECT * FROM USER_ERRORS” statement.

SELECT ObjectName, ObjectType, Status FROM User_Objects WHERE ObjectType = 'PROCEDURES';

OR

SELECT Object_Name, Object_Type, Status FROM User_Objects WHERE ObjectType = “FUNCTION”;



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EXPLAIN HOW TO CREATE FUNCTION? DETAILING:

Syntax: CREATE OR REPLACE FUNCTION <Function Name> (Argument IN Data type...) RETURN <Data type> {IS, AS}

Variable declarations; Constant declarations;

BEGIN PL/SQL subprogram body;

EXCEPTION Exception PL/SQL blocks;

END;

Function also needs pl/sql block to call it.

Declare

Variable declaration

Begin

Variable=call function ();

Subprogram body; End;



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Keywords and Parameters The keywords and the parameters used for creating database functions are

explained below:

REPLACE

Recreates the function if it already exists. This option is used to change the definition of an existing function without dropping, recreating and re-granting object privileges previously granted on it. If a function is redefined, Oracle recompiles it. Function

Is the name of the function to be created? Argument

Is the name of an argument to the function? Parentheses can be omitted if no arguments are present. IN

Indicates that the parameter will accept a value from the user. RETURN data type

Is the data type of the function's return value? Because every function must return a value, this clause is required. It supports any data type supported by PL/SQL. PL/SQL

subprogram body

Is the definition of function consisting of PL/SQL statements.

EXAMPLE: create or replace function get_deptnm(vempno in

number) return number is mdeptnm varchar2(10);

begin select dept.deptnm into mdeptnm from emp,dept where dept.deptno=emp.deptno and emp_no=vempno; return(mdeptnm);

end;



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DELETING A STORED PROCEDURE OR FUNCTION




2 DIFFERENCE BETWEEN PROCEDURE AND FUNCTION

PROCEDURE SHOULD RETURN VALUE AND FUNCTION MUST RETURN VALUE

3 REPLACE MEANS WE CAN OVERWRITE THE FUNCTION OR PROCEDURE

4 HOW MANY BLCOK ARE IN FUNCTION

2

declare

meno number(3);

dnm varchar2(10);

begin

meno:=&meno;

dnm:=get_deptnm(meno);

dbms_output.put_line(‘Employee No. : ‘ || meno || ‘ Department Name : ‘ || dnm);

end;

Syntax: DROP FUNCTION <Function Name>;



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EXPLAIN HOW TO CREATE PROCEDURE? DETAILING:

Keywords and Parameters The keywords and the parameters used for creating database procedures are

explained below:

REPLACE Recreates the procedure if it already exists. This option is used to change the definition of an existing procedure without dropping, recreating and re-granting object privileges previously granted on it. If a procedure is redefined the Oracle engine recompiles it.

Procedure Is the name of the procedure to be created?

Argument Is the name of an argument to the procedure? Parentheses can be omitted if no arguments are present.

IN Indicates that the parameter will accept a value from the user.

OUT Indicates that the parameter will return a value to the user.

IN OUT Indicates that the parameter will either accept a value from the user or return a value to the user.

Data type Is the data type of an argument? It supports any data type supported by PL/SQL.

PL/SQL body Is the definition of procedure consisting of PL/SQL statements.

Procedures can be executed with EXECUTE statement.

Syntax: CREATE OR REPLACE PROCEDURE <Procedure Name> (Argument {IN, OUT, IN OUT) Data Type ...) {IS, AS}

Variable declarations; Constant declarations;

BEGIN PL/SQL subprogram body;

EXCEPTION Exception PL/SQL blocks;

END;



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In the above example, value of employee number is passing to search_employee procedure through PL/SQL block and value of two OUT parameters vename and vjob will return back to the calling block and stored in mename and mjob respectively.

DELETING A STORED PROCEDURE

A procedure can be deleted by using the following syntax

Syntax: Execute procedure name;

create or replace procedure search_employee(vempno in number, vename out varchar2, vjob out varchar2) is begin

select ename,job into vename,vjob from emp where emp_no=vempno; end;

declare mename emp.ename%type; mjob emp.job%type; mempno number := 101;

begin search_employee(mempno,mename,mjob); dbms_output.put_line('Employee # : ' || mempno); dbms_output.put_line('Name : ' || mename || ' Job ' || mjob);

end;

Syntax: DROP PROCEDURE <Procedure Name>;



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2 PROCEDURE AND FUNCTION ARE STORE IN_______

SYSTEM TABLE

3 PROCEDURE AND FUCNTION COMPILE AUTOMATICALLY

YES

EXPLAIN PACKAGE WITH EXAMPLE. DETAILING:-

A package is an Oracle object, which holds other objects within it.

Objects commonly held within a package are procedures, functions, variables, constants, cursors and exceptions.

The tool used to create a package is SQL* Plus.

It is a way of creating generic, encapsulated, re-useable code.

A package once written and debugged is compiled and stored in an Oracle Database.

All users who have executed permissions on the Oracle Database can then use the package.

A package has usually two components:



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1. Package specification 2. Package body.

A package's specification part declares functions, procedures, global memory

variables, constants, exceptions, cursors, etc. A package's body fully defines procedures, functions, and cursors that are

defined in speciation part.

Packages offer the following advantages:

Packages enable the organization of commercial applications into efficient modules.

Each package is easily understood and the interfaces between packages are simple, clear and well defined.

Packages allow granting of privileges efficiently.

A package's public variables and cursors persist for the duration of the session.

Therefore all cursors and procedures that execute in this environment can share them.

Packages enable the overloading of procedures and functions when required.

Packages improve performance by loading multiple objects into memory at once.

Therefore, subsequent calls to related subprograms in the package require no I/O.

Packages promote code reuse through the use of libraries that contain stored procedures and functions, thereby reducing redundant coding.

Syntax of Package Specification: CREATE OR REPLACE PACKAGE package name IS

Declaration of function; Declaration of procedure; Variable declaration;

END packagename;

Syntax of Package Body: CREATE OR REPLACE PACKAGE BODY packagebodyname IS

Definition of function; Definition of procedure; Variable declaration;

END packagebodyname;



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Execution of Package: When a package is invoked, the Oracle engine performs three steps to execute it:

1. Verify user access: Confirms that the user has EXECUTE system privilege granted for the subprogram

2. Verify procedure validity:

Example: Create or replace package pck_employee is

Function get_deptnm (vempno in number) return number is; Procedure search_employee (vempno in number, vename out varchar2, vjob out varchar2) is;

End pck_employee;

Create or replace package body pck_employee is Function get_deptnm (vempno in number) return number is mdeptnm varchar2 (10); begin

Select dept.deptnm into mdeptnm from emp,dept where dept.deptno=emp.deptno and emp_no=vempno; Return (mdeptnm);

end;

Procedure search_employee (vempno in number, vename out varchar2, vjob out varchar2) is begin

Select ename, job into vename, vjob from emp where emp_no=vempno; end;

end pck_employee;



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Checks with the data dictionary to determine whether the procedure and functions used in package are valid or not.

3. Execute: The package subprograms are executed.


1. PACKAGE MEANS? ORACLE OBJECT

2 CAN PACKAGE HOLD OTHER OBJECT WITH IN IT?

YES

3 HOW MANY TYPES OFPACKAGE

2

WHAT IS TRIGGER? EXPLAIN TYPES OF TRIGGER. DETAILING-

Database triggers are database objects created via the SQL* Plus tool on the client and stored on the Server in the Oracle engine's system table.

These database objects consist of the following distinct sections: A named database event A PL/SQL block that will execute when the event occurs

The Oracle engine allows the procedures that are implicitly executed by the user when an insert, update or delete is issued against a table.

These procedures are called database triggers.

The major issues that make these triggers standalone are that, they are fired implicitly (i.e. internally) by the Oracle engine itself and not explicitly called by the user.

Use of Trigger:

A trigger can permit DML statements against a table only if they are issued, during regular business hours or on predetermined weekdays

A trigger can also be used to keep an audit trail of a table (i.e. to store the modified and deleted records of the table) along with the operation performed and the time on which the operation was performed

It can be used to prevent invalid transactions.

Syntax:

Packagename.subprogram name;



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Enforce complex security authorizations.

A trigger has three basic parts:

A triggering event or statement

A trigger restriction

A trigger action

Triggering Event or Statement

It is a SQL statement that causes a trigger to be fired.

It can be INSERT, UPDATE or DELETE statement for a specific table. (i.e. Table write operations)

Trigger Restriction

A trigger restriction specifies a Boolean (logical) expression that must be TRUE for the trigger to fire.

A trigger restriction is specified using a WHEN clause.

In short, when the expression given with WHEN true then only trigger action becomes executes for triggering event.

Trigger Action

A trigger action is the PL/SQL code to be executed when a triggering event fires and any trigger restriction (if any) evaluates to TRUE.

The PL/SQL block can contain SQL and PL/SQL statements.

For row triggers, the PL/SQL block can access column values by using :new and :old keyword.

TYPES OF TRIGGERS

There are mainly two types of triggers: 1. Row Triggers 2. Statement Triggers

Row Triggers

A row trigger is fired each time a row in the table is affected by the triggering statement.

Note: The PL/SQL block cannot contain transaction control SQL statements like COMMIT, ROLLBACK, and SAVEPOINT in trigger



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For example, if an UPDATE statement updates 5 rows of a table, a row trigger is fired once for each row means it fires 5 times.

If the triggering statement affects no rows, the trigger is not executed at all.

Row triggers should be used when some processing is required whenever a triggering statement affects a single row in a table.

Statement Triggers

A statement trigger is fired once on behalf of the triggering statement, independent of the number of rows the triggering statement affects.

Even if no rows are affected, trigger fired.

Statement triggers should be used when a triggering statement affects rows in a table but the processing required is completely independent of the number of rows affected.

Row Trigger and Statement Triggers are further classified into

1. Before Trigger 2. After Trigger.

Before Triggers BEFORE triggers execute the trigger action before the triggering statement. These types of triggers are commonly used in the following situations:

BEFORE triggers are used when the trigger action should determine whether or not the triggering statement should be allowed to complete.

By using a BEFORE trigger, user can eliminate unnecessary processing of the triggering statement.

BEFORE triggers are used to derive specific column values before completing a triggering INSERT or UPDATE statement.

After Triggers AFTER trigger executes the trigger action after the triggering statement is executed. These types of triggers are commonly used in the following situations:

AFTER triggers are used when the triggering statement should complete before executing the trigger action.

If a BEFORE trigger is already present, an AFTER trigger can perform different actions on the same triggering statement

BEFORE statement trigger



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Before executing the triggering statement, the trigger action is executed.

BEFORE row trigger Before modifying each row affected by the triggering statement and before applying appropriate integrity constraints, the trigger is executed.

AFTER Statement Trigger

After executing the triggering statement and applying any deferred integrity constraints, the trigger action is executed.

AFTER Row Trigger After modifying each row affected by the triggering statement and applying appropriate integrity constraints, the trigger action is executed for the current row. Unlike BEFORE row triggers, AFTER row triggers have rows locked.


1. WHICH TOOL USE IN CREATE TORGGER

SQL*PLUS

2 HOW MANY TYPES OF TIRGGER

2

3 WHATIS TIRGGER? WE CAN CREATE SEQURITY PURPOSE.

EXPLAIN TRIGGER WITH EXAMPLE. DETAILING:-

Syntax: CREATE OR REPLACE TRIGGER <trigger name>

BEFORE, AFTER {DELETE, INSERT, UPDATE [OF Column ...]} ON <table name> [REFERENCING {OLD AS old, NEW AS new}] [FOR EACH ROW [WHEN Condition] ]



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The keywords and the parameters used for creating database triggers are explained below:

OR REPLACE

Recreates the trigger if it already exists. This option can be used to change the definition of an existing trigger without requiring the user to drop the trigger first. Trigger Name

Is the name of the trigger to be created? BEFORE

Indicates that the Oracle engine fires the trigger before executing the triggering statement. AFTER

Indicates that the Oracle engine fires the trigger after executing the triggering statement. DELETE

Indicates that the Oracle engine fires the trigger whenever a DELETE statement deletes any row of table.

INSERT

Indicates that the Oracle engine fires the trigger whenever an INSERT statement inserts any row in table. ON

Specifies the name of the table, which the trigger is to be created. A trigger cannot be created on a table in the schema SYS.

FOR EACH ROW

Designates the trigger to be a row trigger. The Oracle engine fires a row trigger once for each row that is affected by the triggering statement and meets the optional trigger constraint defined in the WHEN clause. If this clause is omitted the trigger is a statement trigger.

REFERENCING

Specifies correlation names. Correlation names can be used in the PL/SQL block and WHEN clause of a row triggers to refer specifically to old and new values of the current row.

WHEN

Specifies the trigger restriction. The trigger restriction contains a SQL condition that must be satisfied for the Oracle engine to fire the trigger. This condition must contain correlation names and cannot contain a query.

Syntax: DROP TRIGGER <trigger name>;

declare oper varchar2(8);

begin if updating then

oper := 'update'; end if;



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645



1. WHICH TOOL USE IN CREATE TORGGER

SQL*PLUS

2 HOW MANY TYPES OF TIRGGER

2

3 WHATIS TIRGGER? WE CAN CREATE SEQURITY PURPOSE.

EXPLAIN USER DEFINED DATATYPE IN ORACLE. DETAILING: Create Type command is used to create an abstract data type or user defines data type.

Syntax: Create type <type name> as object ( Name Data type (size), Name Data type (size), …, … );



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


The create type command is the most important command in object-relational databases.

It will represented as having four attributes, named street, city, state, and pin using the defined data types and lengths for each column.

You can also use the user defined data type in creation of other user define data type.

Use of Data type:

Example: Create type add_type as object ( street varchar2(50), city varchar2(20), state varchar2(20), pin number(6) );

Example: Create type person_type as object ( name varchar2(20), add1 add_type );

Example: Create table customer ( cust_id number(3), person person_type );



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


Inserting records in table contain user define data type:

Ex. Insert into customer values (1, person_type(‘Neel’,address_type(3, south extension, New-Delhi, Delhi, 110001)));

Selecting records from table contain user define data type:

Ex. Select cust_id, c.person.name,c.person.address.city from customer c;


1. ABSTRACT DATA TYPE IS ALSO CALLED____

USER DEFINE DATA TYPE

2 CREATE TYPE COMMAND ALSO CALLED_____

USER DEFINE DATA TYPE

3 CAN THIS DATA TYPE PUT IN TABLE?

YES

EXPLAIN VARRAY WITH EXAMPLE. DETAILING-:



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


Varray is known as collector means sets of elements that are treated as part of a single row.

A varying array allows you to store repeating attributes of a record in a single row.

For example, suppose Dona wants to track which of her tools were borrowed by which of her worker.

You should create a table to keep track of this.

Thus, if a single worker borrowed three tools, the worker’s name would be repeated in each of the three records.

Collection such as varying arrays allows you to repeat only those column values that change, potentially saving storage space.

Creating a Varray:

You can create varray based on either an abstract datatype or one of the oracle standard data type.

To create varray use the ‘as varray ( )’ clause of the create type command.

Example: Create table borrower ( name varchar2(25), tool varchar2(25) );

Syntax: Create or replace type <type name> as varray (size) of data type (size)

Example: Create or replace type tools_va as varray (5) of varchar2 (20);

Example: Create table borrower ( name varchar2(25), tool tools_va );



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


Inserting records into Varray ( ):

When a data type is created, the database automatically creates a method called a constructor method for the data type.

Since a varying array is an abstract data type, we need to use constructor method to insert records into tables that use varying arrays.

This insert into first specifies the value of the name column.

Because the name column is not a part of abstract data type.

Selecting data from varray ( )

The maximum number of entries per row, called its LIMIT, and the current number of entries per row, called its COUNT.

This query cannot be performed directly vie a SQL select statement.

To retrieve the COUNT AND LIMIT from varray you need to use PL/SQL.

ONE WORD QUESTION AND ANSWER

Example: Insert into borrower values (‘Neel’,tools_va(‘hammer’,’ax’,’sledge’,null,null));

Example: Declare Cursor bor_cur is Select * from borrower; Begin For bor_rec in bor_cur Loop Dbms_output.put_line(‘Name’ || bor_rec.name); For I in 1..bor_rec.tools.count Loop Dbms_output.put_line(bor_rec.tools(i)); End loop; End loop; End;



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


SR.NO QUESTION ANSWER 1. VARRAY MEANS____- COLLECTOR

2 HOW MANY TYPES OF ATTRIBUTE ARE STORE IN

ONE LINE

255

3 VARRAY MEANS____ VARRIYING ARRAY.

EXPLAIN NESTED TABLE WITH EXAMPLE. DETAILING:

Varray have a limited number of entries, a second type of collector is “Nested Table”.

Nested Table has no limit on the number of entries per row.

A nested table is, as its name implies, a table within a table.

It is a table that is represented as a column within another table.

You can have multiple rows in the nested table for each row in the main table.

Syntax : Create or replace type < table name> as table of <user define type> Create table <table name> ( columnname datatype(size), columnname nested table ) nested table <column name contain nested table data type> store as <table name>;



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645


Varray cannot be indexed, while nested table can be indexed.

In varray, the data in the array is stored with the rest of the data in the table.

While in nested table, the data may be stored out-of-line.

SELECTING ROW FROM NESTED TABLE

To support queries of the columns and rows of a nested table, oracle provides a special keyword, THE.

Example: Create or replace type stud_ty as object ( name varchar2(15), add1 varchar(30), city varchar2(15) );

create type stud_nt as table of stud_ty; create table studrec (

stream varchar2(15), studdet stud_nt

) nested table studdet store as stud_tab;

Inserting record into nested table: Insert into studrec values (‘BCA4’,stud_nt(stud_ty(‘xyz’,’jagnath plot’,’rajkot’), stud_ty(‘abc’,’kalawad road’,’rajkot’), stud_ty(‘pqr’,’university road’,’rajkot’) ));

EXAMPLE: Select name from the (select studdet from studrec where stream like 'BCA4')



Ph.No–(0281)2440478,2472590 Ph.No–(0281)2471645



1. NESTED TABLE MEANS COLLECTOR

2 NESTED TABLE ALSO CALLED___

TABLE WITHIN TABLE

3 CAN LIMIT APPLY IN N.T. NO

CH-4:- PL/SQL

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