Introduction to PL/SQL

Francis Thottungal

The outline

• The basic PL/SQL code structure is :• DECLARE -- optional, which declares and define

variables, cursors and user-defined exceptions.• BEGIN -- mandatory• - SQL statements• - PL/SQL statements• EXCEPTION -- optional, which specifies what

actions to take when error occurs.• END; -- mandatory

Hello World

DECLAREv1 Varchar2(50);

BEGIN v1 := ‘Hello World’; DBMS_OUTPUT.PUT_LINE('v1=' || v1); END;

SQL Plus UsageAt command prompt:C:>SQL SET SERVEROUTPUT ONDECLARE

v1 Varchar2(50);

BEGIN v1 := ‘Hello World’; DBMS_OUTPUT.PUT_LINE('v1=' || v1); END;

/Note that a PL/SQL block is terminated by a slash /

or a line byitself.

EXAMPLE-2

DECLAREv1 NUMBER(3);

BEGIN v1 := 3; DBMS_OUTPUT.PUT_LINE('v1=' || v1); END;

Handling Variables• Variables must be declared first before the usage. The

PL/SQL variables can be a scalar type such as DATE, NUMBER, VARCHAR(2), DATE, BOOLEAN, LONG and CHAR, or a composite type, such array type VARRAY.

• Only TRUE and FALSE can be assigned to BOOLEAN type of variables.

• AND, OR, NOT operators can be used to connect BOOLEAN values.

• % TYPE attribute can be used to define a variable which is of type the same as a database column's type definition.

• Users can customize the variable types by using TYPE ... IS ... statement.

The following code block illustrates the use of TYPE..IS... and VARRAY. In this sample, a type v_arr is defined as an variable array of maximum 25 elements which are of type NUMBER(3). Then a variable v1 is defined as type v_arr . This sample code also demonstrates the use of %TYPE attribute.

DECLARETYPE v_arr IS VARRAY(25) of NUMBER(3);

v1 v_arr;v_empno employee.empno%TYPE;

BEGIN v1(2) := 3;

DBMS_OUTPUT.PUT_LINE('The Value of v1(2) = ' || v1(2)); v_empno := 4;END;

Programming Guidelines• Single-line comments are prefixed with two dashes --.• Multiple-line comments can be enclosed with the

symbols /* and */.• Variables and function identifiers can contain up to 30

characters, and should not have the same name as a database column name.

• Identifiers must begin with an alphanumerical character.• SQL functions can be used in PL/SQL.• Code blocks can be nested and unqualified variables can

locally scoped.• It is recommended that variable names are prefixed by v_,

and parameter names in procedures/functions are prefixed by _p.

DECLARE v_sal employee.sal%TYPE;BEGIN

INSERT INTO employee VALUES (6, 'TOM LEE', 10000);

UPDATE employee SET sal = sal + 5000 WHERE empno = 6;

• SELECT sal INTO v_sal FROM employee WHERE empno = 6;

DBMS_OUTPUT.PUT_LINE('Salary increased to ' || v_sal); DELETE FROM employee WHERE empno = 6; COMMIT;

END;

/

• A SQL cursor is a private Oracle SQL working area. There are two types of SQL cursor: implicit or explicit cursor. The implicit cursor is used by Oracle server to test and parse the SQL statements and the explicit cursors are declared by the programmers.

• Using the implicit cursor, we can test the outcome of SQL statements in PL/SQL. For example,

• SQL%ROWCOUNT, return the number of rows affected;• SQL%FOUND, a BOOLEAN attribute indicating whether the

recent SQL statement matches to any row;• SQL%NOTFOUND, a BOOLEAN attribute indicating whether

the recent SQL statement does not match to any row;• SQL%ISOPEN, a BOOLEAN attribute and always evaluated

as FALSE immediately after the SQL statement is executed.

DECLARECURSOR csr_ac (p_name VARCHAR2) IS

SELECT empno, name, salFROM employeeWHERE name LIKE '%p_name%';

BEGINFOR rec_ac IN csr_ac ('LE')

LOOP DBMS_OUTPUT.PUT_LINE(rec_ac.empno || ' ' ||rec_ac.name || ' '||v_sal); END LOOP ;

CLOSE csr_ac;END;/