Oracle: PLSQL Introduction

Oracle: PLSQL Introduction

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  1Using ORACLE®Introduction toPL/SQL
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  DATA DEFINATION LANGUAGEOracleEnginePL/SQL ENGINE:2PL/SQL stands for Procedural Extension to Structured Query Language.PL /SQL support is provided in Oracle from versions > 6;PL/SQL is used to provide users with the ability to use variables, loops , function etc in the database.SQL can be combined easily into the PL/SQL code .Since the PL/SQL program is processed by the PL/SQL Statement Executor ,it reduces the load on Oracle thus making it perform faster.
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  3Anonymous BlockPL/SQL usesa block structure hence making it easier to write and maintain code.PL/SQL provides us with the following:Variables and constants.Loops and conditional constructs.Functions and Procedure that enable code reusability.Exception handling .The Anonymous Block ,the basic PL/SQL code is as follows: <<label>> [ DECLARE ] TYPE / item / FUNCTION / PROCEDURE declarations or variables. BEGIN Statements (both SQL and PL/SQL) [ EXCEPTION ] EXCEPTION handlers to handle the exception END label;
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  4Anonymous BlockLet uswrite an example Anonymous block.DECLAREname varchar2[20];BEGINname := ‘Larry’;DBMS_OUTPUT.PUT_LINE(‘The name is : ‘ || name);ENDThe above anonymous block print the name ‘Larry'. Key points to be highlighted here are:The variable name must follow rules similar to that of declaring Tables in SQL and the data type with size be mentioned.The := operator is the assignment operator in PL/SQL.The DBMS_OUTPUT.PUT_LINE prints text enclosed in ( ) .Here we use a ‘||’ concatenation operator to join the string and variable.
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  5VariablesThe various datatypes in PL/SQL are :LOB refers to large object. It could be of the type BINARY LARGE OBJECT (BLOB) or CHARACTER LARGE OBJECT (CLOB) to store image or audio in binary format (BLOB) or a text file (CLOB) up to the size of 4 GIGABYTES.BFILE refers to an external file to be stored in a database. A variable must be declared in the “DECLARE” block as: VARIABLE_NAME DATATYPE[SIZE]; A variable may be initialized when declared (otherwise set to NULL) VARIABLE_NAME DATATYPE[SIZE]:= VALUE; We may also define a variable to not hold null values. VARIABLE_NAME DATATYPE[SIZE] NOT NULL := VALUE;
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  6%TYPE and %ROWTYPEWe can declare a variable to have a data type of any column or another variable using the %TYPE attribute which is prefixed with the table and column or variable name.SYNTAX: VARIABLE _NAME TABLE_NAME.COLUMN_NAME[VARIABLE_NAME]%TYPE ;EXAMPLE: name InfoTable.name%TYPE;The %ROWTYPE attribute is used to declare a variable to hold an entire row which is a collection of multiple columns of a table.SYNTAX: VARIABLE _NAME TABLE_NAME %ROWTYPEEXAMPLE: name InfoTable%ROWTYPE;
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  7BIND/HOST VARIABLESBind variablesare the variables that are created in the host environment hence also called as host variable. The features of a bind variable are:Unlike normal variables the memory used by a bind variable is not cleared when the PL/SQL block execution is complete.Can be accessed outside the block by other PL/SQL and SQL code.Declared using a VARIABLE keyword and above the “DECLARE” block.While usage they are referred wit a prefixed : symbolSYNTAX:VARIABLE variable_name DATATYPE[SIZE];EXAMPLE:VARIABLE eage NUMBER; BEGIN SELECT age INTO :eage FROM InfoTable WHERE name = ‘bill’; END Only character array variables need to be given a size.
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  8Substitution VariablesWe caneither hard code the values of variable or accept the values from the user. To accept a value from the user , it has to be declared as a SUBSTITUTION VARIABLE. Substitution variables when used accept value from user.SYNTAX:VARIABLE variable_name DATATYPE[SIZE] := &variable_name;EXAMPLE :VARIABLE age NUMBER; DECLAREename VARCHAR(20) := &ename; BEGIN SELECT age INTO eage FRM InfoTable WHERE name = ename; END;
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