Oracle 10g SQL-pl SQL

8/2/2019 Oracle 10g SQL-pl SQL

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Oracle 10g SQL/PL SQL


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Agenda

PL/SQL - Introduction - Benefits and Advantages PL/SQL Block - Declare, Begin and Exception Section Block Types PL/SQL Placeholders - Variables,Constants,Records DBMS_OUTPUT.PUT_LINE Writing Executable Statements Interacting with Oracle Server Conditional Statements in PL/SQL Iterative Control Cursors Handling Exceptions Procedures and Functions

Packages Triggers


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What is PL/SQL?

PL/SQL stands for Procedural Language extension of SQL PL/SQL is a combination of SQL along with the procedural features of

programming languages. It was developed by Oracle Corporation in the early 90s to enhance

the capabilities of SQL.


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Application

OtherDBMSs

Application

Oracle with

PL/SQL

SQL

SQL

SQL

SQL

SQL

IF...THEN

SQL

ELSE

SQL

END IF;

SQL

Benefits of PL/SQL


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Advantages of PL/SQL

Block Structures Blocks of code which can be nested inside each other

Procedural Language Capability Use of Conditional Statements (if-else) / loops like

(FOR/WHILE)

Better Performance Processes multiple SQL statements simultaneously as a

single block Reduces Network Traffic

Error Handling Handles Errors/Exception effectively during execution of

PL/SQL program

Exception Caught can be used to take specific action


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A Simple PL/SQL Block

Each PL/SQL program consists of SQL and PL/SQL

statements which from a PL/SQL block A PL/SQL Block consists of three sections:

The Declaration section (optional). The Execution section (mandatory). The Exception (or Error) Handling section (optional).

DECLARE

BEGIN

END;

Exception Handling

EXCEPTION

Variable Declaration

Program Execution


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PL/SQL Block DECLARE Section

Starts with the optional reserved keyword DECLARE

Used to declare any placeholders Placeholders can be

Variables User Defined Exceptions Cursors

Constants Each Declaration/Assignment ends with a semi-colon

E.g DECLAREv_variable VARCHAR2(5);


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PL/SQL Block Exception Section

Optional Section; starts with a reserved keywordexception

Used for handling errors in the program section forthe PL/SQL block to terminate gracefully

Any unhandled exceptions ends the program abruptly Each statement ends with a semicolon

E.g EXCEPTIONWHEN exception1 [ or exception2 ..] THEN

statement1;

statement2;

WHEN exception3 THEN

statement3;

WHEN OTHERS THEN

statement4;


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Block Types in PL/SQL

[DECLARE]

BEGIN--statements

[EXCEPTION]

END;

PROCEDURE name

IS

BEGIN--statements

[EXCEPTION]

END;

FUNCTION name

RETURN datatype

ISBEGIN

--statements

RETURN value;

[EXCEPTION]

END;

ANONYMOUS PROCEDURE FUNCTION


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PL/SQL Placeholders Variables Placeholders are temporary storage of data which

can be any Variables, Constants and Records

PL/SQL Variables Declare and Initialise variables in the DECLARE Section Assign new values to variables in the Executable Section Syntax :

variable_name datatype [NOT NULL := value ];

Methods DECLARE

n_salary number (6);

v_dept varchar2(10) NOT NULL := HR Dept;

BEGIN

SELECT column_name INTO variable_name FROMtable_name [WHERE condition];


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PL/SQL Placeholders Variables contd

Types of Variables PL/SQL Variables

Scalar Holds a Single Value CHAR,VARCHAR2,LONG,NUMBER,BINARY_INTEGER,BOOLEA

N DATE,TIMESTAMP, %TYPE Attribute - Syntax : identifier Table1.column%TYPE;

Composite or Collections %ROWTYPE, RECORD, VARRAY , NESTED TABLE, TABLE

LOB ( Large Objects ) BLOB,CLOB

Non PL/SQL Variables

Bind and Host Variables Avoid HardParsing when called from external

applications


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PL/SQL Placeholders Constants Value used in the PL/SQL block that remains

unchanged in the whole program

General Syntax for Declaring Constants

constant_name CONSTANT datatype := VALUE;

Value should be assigned when you declare it

Assigning or Re-assigning the value in the execsection causes an error


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PL/SQL Placeholders - Records Records are composite data types ( Combination of Scalar Data types) Can be visualized as a row of data First Define a Composite Datatype and then declare a record for that type General Syntax

TYPE record_type_name IS RECORD(first_col_name column_datatype, second_col_name column_datatype, ...);

col_name table_name.column_name%type; record_name table_name%ROWTYPE;

Advantages No need to explicitly declare variables for all the columns of the table Altering the column specification does not require modifying the code

Disadvantages ROWTYPE declaration fields will create for all columns of the table

Creating a RECORD only creates a data type. Values are required to be

assigned to record to use them


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PL/SQL Placeholders Records contdSyntax of Records Usage

TYPE record_type_name IS RECORD(column_name1 datatype, column_name2

datatype, ...);

Define a composite datatype, where each field isscalar.

col_name table_name.column_name%type; Dynamically define the datatype of a columnbased on a database column

record_name record_type_name; Declare a record based on a user-defined type.

record_name table_name%ROWTYPE; Dynamically declare a record based on an entirerow of a table. Each column in the tablecorresponds to a field in the record.


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PL/SQL Placeholders Records contd..

Passing Values To and From a Record

Syntax Usage

record_name.col_name := value; To directly assign a value to a specificcolumn of a record.

record_name.column_name := value; To directly assign a value to a specificcolumn of a record, if the record isdeclared using %ROWTYPE.

SELECT col1, col2 INTOrecord_name.col_name1,record_name.col_name2 FROMtable_name [WHERE clause];

To assign values to each field of arecord from the database table.

SELECT * INTO record_name FROMtable_name [WHERE clause];

To assign a value to all fields in therecord from a database table.

variable_name :=record_name.col_name;

To get a value from a record columnand assigning it to a variable


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DBMS_OUTPUT.PUT_LINE

Oracle Supplied packaged procedure

An alternative for displaying data from PL/SQL Block Must be enabled in SQLPLUS session using thecommand

SET SERVEROUTPUT ON

DECLARE

v_sal NUMBER(9,2) := 10000;

BEGIN

v_sal := v_sal/12;

DBMS_OUTPUT.PUT_LINE ('The monthly salary is ' ||

TO_CHAR(v_sal));END;

/


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Writing Executable Statements Guidelines for Identifiers

Variables can contain upto 30 chars and begin with a alphabetic character Can contain numbers,dollarsigns,underscore Cannot contain hyphens,slashes and spaces Should not be a reserved word Character and Date literals must be enclosed in single quotes Single-line comments with two dashes ( --) Multi-line comments with /* .. */

Programming Guidelines

Documenting Code with comments Following naming conventions for the code Enhancing Readability by indenting

SQL Functions can be used in procedural statements except DECODE Group Functions

E.g v_ename := LOWER(v_ename); Datatype Conversion functions to be used before assigning

v_date := TO_DATE ('January 13, 2001','Month DD, YYYY');


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Interacting with Oracle Server SELECT Statements in PL/SQL

SELECT select_list INTO [ variable_names ] FROM table1WHERE [ Filter Criteria ]

Queries must return only a single row to avoid exceptions

Manipulating Data to database using DML Commands in PL/SQL Insert Statements in PL/SQL Update Statements in PL/SQL

Delete Statements in PL/SQL Transaction Control Statements in PL/SQL

Use of COMMIT/ROLLBACK to terminate a transaction explicitly

Sample Exercise Playaround with Employee Table using PL/SQLsub-programs


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Conditional Statements in PL/SQL PL/SQL supports conditional and iterative statements like other programming

languages IF-THEN-ELSIF- ELSE Statement

IF condition 1 THEN

statement 1; statement 2;

ELSIF condtion2 THEN

statement 3;

ELSEstatement 4;

END IF;

CASE ExpressionCASE selector

WHEN expression1 THEN result1

WHEN expression2 THEN result2

...

WHEN expressionN THEN resultN

[ELSE resultN+1;]


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Iterative Control - Loop Statements Loops repeat a statement or sequence of statements multiple times. Basic Loop Types

Basic Loop

Simple Loop when a set of statements has to be executed at leastonce and should contain a EXIT condition to avoid infinite loop

LOOP

statements;

EXIT [WHEN condition];

END LOOP;

FOR Loop

Execute a condition for a pre-determined number of timesFOR counter IN [REVERSE] lower_bound..upper_bound LOOP

statements

END LOOP;

WHILE Loop

To be used as long as a condition is trueWHILE condition LOOP

statements;

END LOOP;


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Cursors Implicit and Explicit

Temporary work area created in system memorywhen SQL statements are executed

Work area is used to store the data retrieved from thedatabase ( Active Set )

Types of Cursor Implicit

Created automatically when DML and SELECT

statements OPEN/FETCH/CLOSE of Cursor is done automatically

Explicit Created by user when executing SELECT statements OPEN/FETCH/CLOSE should be done manually


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Cursors Implicit Cursor Attribues

Attributes Return Value Example

%FOUND TRUE DML/SELECT INTOstatement affects atleast onerow

FALSE No rows affected

SQL%FOUND

%NOTFOUND FALSE DML/SELECT INTOstatement affects atleast one

rowTRUE No rows affected

SQL%NOTFOUND

%ROWCOUNT Returns the number of rowsaffected by the DMLoperationsINSERT/UPDATE/DELETE

SQL%ROWCOUNT


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Cursors Explicit Cursors

Is a SELECT statement that is explicitly defined in thedeclaration section with a name

General Syntax CURSOR cursor_name IS select_statement;

How to use Explicit Cursors ? DECLARE the cursor in the declaration section OPEN the cursor in the Execution Section

Command : OPEN cursor_name; FETCH the data from cursor into PL/SQL variables or

records in the Execution Section inside a loop FETCH cursor_name INTO record_name

CLOSE the cursor in the Execution Section before you end

the PL/SQL Block. CLOSE cursor_name;


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Cursors Explicit Cursors - Attributes

Use Cursor attributes to control data processing andavoiding errors in OPEN/FETCH/CLOSE statements

Attributes Return Values Example

%FOUND TRUE - if fetch statementreturns at least one row.

FALSE, if fetch statementdoesnt

cursor_name%FOUND

%NOTFOUND TRUE/FALSE cursor_name%NOTFOUND

%ROWCOUNT No.of.rows returned cursor_name%ROWCOUNT

%ISOPEN TRUE/FALSE cursor_name%ISOPEN


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Cursors Explicit Cursors Using Loops

While Loop can be used to get the values from thecursor into a PL/SQL record variable

Most commonly used is the FOR loop Shortcut to process the explicit cursors Implicit Open , Fetch, Exit and Close occurs PL/SQL Record variable is implicitly declared

FOR record_name IN cursor_name LOOP -> Cursor is explicitly declared and used

statements;

END LOOP;

FOR record_name IN ( SELECT .QUERY ) LOOP -> Cursor is implicit declaredstatements;

END LOOP;

Excersise : Print the output of all the employees in a given format using the while and for loop


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Advanced Explicit Cursor Concepts Cursors with parameters

Parameters in cursors makes it more reusable instead of hardcodingCURSOR cursor_name [(parameter_name datatype, ...)]

IS select_statement;

Pass the argument when the cursor is to be openedOpen cursor_name (:variable_name or constant value)

Default Values can be used in the parameters when cursor is declared SELECT FOR UPDATE in Cursors

Used to update values present in the table by obtaining a exclusivelock

FOR UPDATE clause with or without a column name has to bespecified in the declaration

WHERE CURRENT OF clause explicitly mentions to update thecurrent row fetched

Important advantage of using WHERE CURRENT OF is to avoid

using multiple update statements and conditional looping Exercise : Update the joining date of the employee table for all the records

using WHERE CURRENT OF


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Handling Exceptions in PL/SQL

PL/SQL provides feature to handle exceptions in a separate block General Structure of ExceptionEXCEPTION -> Exception Block

WHEN ex_name1 THEN

-Error handling statements

WHEN ex_name2 THEN


WHEN Others THEN


END;

When Exceptions are raised, oracle searches for an appropriate exception

handler in the exception section If none of them are present, then oracle abruptly ends the execution with an

error WHEN OTHERS should always be the last clause in the exception handling

section


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Handling Exceptions Exception Types Exception Types

Named System Exceptions

Automatically raised when there is a Oracle error Known Exception

E.g NO_DATA_FOUND;ZERO_DIVIDE;TOO_MANY_ROWS etc Unnamed System Exceptions

Unknown Exception that are less frequent and oracle does not give ameaningful explanation

Can be avoided using WHEN OTHERS or using PRAGMAEXCEPTION_INIT

PRAGMA EXCEPTION_INIT (exception_var_name,); User-Defined Exceptions

Exceptions based on business rules

Declared in the Declare Section, Explicitly raised in the executionsection,Referenced in the exception section

RAISE_APPLICATION_ERROR

Built in procedure to display the user defined error messageswhose range is between -20000 and -20999

RAISE_APPLICATION_ERROR (error_number,error_message);


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Creating Procedures Named PL/SQL Block to perform any task Contains a Header and a Body

Header consists of name of procedure and parameters orvariables passed to the procedure

Body consists of DECLARATION,BEGIN and EXECUTIONsection

General SyntaxCREATE [OR REPLACE] PROCEDURE proc_name [list of parameters] IS

Declaration section

BEGIN

Execution section

EXCEPTION

Exception section

END

Execute a Stored Procedure using Exec procedure_name inside a BEGIN END; Inside another procedure - procedure_name;

Creating Procedures with parameters


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Creating Procedures with parameters

IN OUT IN OUT

Default Mode Must be Specified Must be Specified

Value is passed to thesub-program

Returned to the callingenvironment

Passed into thesubprogram andreturned

Can be assigned adefault value

Cannot be assigned adefault value

Cannot be assigned adefault value

Actual Parameter canbe a variable or aconstant

Has to be a variable Has to be a variable


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Creating Functions Named PL/SQL block that returns a value The Return General SyntaxCREATE [OR REPLACE] FUNCTION function_name [parameters]

RETURN return_datatype;

IS

Declaration_section

BEGIN

- Execution_section

Return return_variable;

EXCEPTION exception section

Return return_variable;

END;

Executing a Function variable_name := function_name(parameters);

SELECT function_name(parameters); FROM dual;

Select STATEMENTS like any other Oracle defined functions

dbms_output.put_line(function_name);


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Packages - Overview Collection of PL/SQL objects that are grouped together Package can contain

Procedure,Functions,Cursors,Variables,Constants Contains a Package Specification and a Body Package Specification

Contains the definition or specification of all elements in a package Contains Public Variables required for accessing across the

elements of the package Package Body

Definition of all the elements of the package defined in thespecification

Private procedures/functions which are not defined in the packagespecification

Public Constructs can be referenced across the Oracle serverenvironment

Private Constructs can be referenced only by other constructs of thesame package

Package Specification can exist without a body but not vice-versa


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Packages Overview contd General Syntax for Package Specification

CREATE OR REPLACE PACKAGE package_nameIS

public type and item declarations

sub-programs specifications

END package_name;

Package Body SyntaxCREATE OR REPLACE PACKAGE BODY package_name

IS

[ declarations of variables and types ]

[ specification and SELECT statement of cursors ]

[ specification and body of modules ]

[ BEGIN

executable statements ]

[ EXCEPTION

exception handlers ]

END [ package_name ];

Invoking Package procedures

EXECUTE package_name.procedure_name(paramter values); EXECUTE schema_name.package_name.procedure_name(parameter vaues);


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Advantages of Packages

Modularity : Encapsulate logically relatedprogramming structures

Easier Application Design : Having a Specificationand Body

Hiding Information Public and Private Constructs

Better Performance Entire package is loaded into the memory when package is

first referenced

Overloading Multiple Sub-programs with the same name


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Triggers PL/SQL block structure is fired implicitly when a DML statement is

executed on a database table/view Types of Trigger

Row level - Triggered for each row updated , inserted or deleted Statement level Triggered for each sql statement executed Before and After Triggers Perform action before or after triggering action

General SyntaxCREATE [OR REPLACE ] TRIGGER trigger_name

{BEFORE | AFTER | INSTEAD OF } ======= Events

{INSERT [OR] | UPDATE [OR] | DELETE} === DML Action

[OF col_name] ======= Column name or List

ON table_name ====== Table Name

[FOR EACH ROW] ==== Row Level or Statement Level

WHEN (condition) ==== Row Level Trigger Condition

BEGIN

--sql statements

END;


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Triggers contd Handling Multiple Situations using Conditional Predicates

Combine Several Triggering events into one by using special conditional predicatesINSERTING,UPDATING,DELETING

Usage

IF [DELETING|INSERTING|UPDATING] THEN..

END IF;

Old and New Qualifiers Applicable only for ROW Triggers OLD and :NEW to access the before and after value of the column value that is modified

:OLD. and :NEW.

Guidelines for Designing Triggers Perform related action based on specific operation Do not design triggers to duplicate functionality of Oracle

E.g Integrity Checks Avoid Excessive use of triggers which can be difficult to maintain

Firing Sequence of Triggers

BEFORE Statement Trigger BEFORE Row Trigger AFTER Row Trigger AFTER Statement Trigger


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Oracle 10g SQL-pl SQL

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