2. DATA DEFINATION LANGUAGE Oracle Engine PL/SQL ENGINE: 2 PL/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.
3. 3 Anonymous Block PL/SQL uses a 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;
4. 4 Anonymous Block Let us write an example Anonymous block. DECLARE name varchar2[20]; BEGIN name := ‘Larry’; DBMS_OUTPUT.PUT_LINE(‘The name is : ‘ || name); END The 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.
5. 5 Variables The various data types 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;
6. 6 %TYPE and %ROWTYPE We 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 %ROWTYPE EXAMPLE: name InfoTable%ROWTYPE;
7. 7 BIND/HOST VARIABLES Bind variables are 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 : symbol SYNTAX: 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.
8. 8 Substitution Variables We can either 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; DECLARE ename VARCHAR(20) := &ename; BEGIN SELECT age INTO eage FRM InfoTable WHERE name = ename; END;
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