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 DECLARE v1 Varchar2(50); BEGIN v1 := ‘Hello World’; DBMS_OUTPUT.PUT_LINE('v1=' || v1); END;

SQL Plus Usage At command prompt: C:>SQL SET SERVEROUTPUT ON DECLARE 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 DECLARE v1 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. DECLARE TYPE 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 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.

DECLARE CURSOR csr_ac (p_name VARCHAR2) IS SELECT empno, name, sal FROM employee WHERE name LIKE '%p_name%'; BEGIN FOR 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; /