PL/SQL A BRIEF OVERVIEW DAVID WILSON

PL/SQL User’s Guide and Reference PL/SQL User’s Guide and Reference

MAIN FEATURES Block Structure Block Structure Variables and Constants Variables and Constants Cursors Cursors Control Structures Control Structures Modularity Modularity Data Abstraction Data Abstraction Information Hiding Information Hiding Error Handling Error Handling

Block Structure DECLARE – declaration of variables, constants, and subprograms DECLARE – declaration of variables, constants, and subprograms BEGIN – statements BEGIN – statements EXCEPTON – exception handlers EXCEPTON – exception handlers END END

VARIABLES and CONSTANTS May have any SQL or PL/SQL datatype May have any SQL or PL/SQL datatype Composite datatypes allowed Composite datatypes allowed Three methods of assigning values Three methods of assigning values Simple assignment Simple assignment Fetch value from database Fetch value from database Return value from subprogram Return value from subprogram May be declared as constant May be declared as constant

ASSIGNMENT EXAMPLES tax := price * tax_rate; valid_id := FALSE; SELECT sal * 0.10 INTO bonus FROM emp WHERE empno = emp_id; credit_limit CONSTANT REAL := ;

ASSIGNMENT EXAMPLES DECLARE my_sal REAL(7,2); PROCEDURE adjust_salary (emp_id INT, salary IN OUT REAL) IS... BEGIN SELECT AVG(sal) INTO my_sal FROM emp; adjust_salary(7788, my_sal); -- assigns a new value to my_sal

CURSORS Implicit vs. Explicit Implicit vs. Explicit FOR loops FOR loops Attributes Attributes %TYPE %TYPE %ROWTYPE %ROWTYPE DECLARE CURSOR c1 IS SELECT ename, sal, hiredate, job FROM emp; emp_rec c1%ROWTYPE; -- declare record variable that represents a row fetched from the emp table

CONTROL STRUCTURES IF – THEN –ELSE IF – THEN –ELSE CASE CASE FOR – LOOP FOR – LOOP WHILE – LOOP WHILE – LOOP EXIT – WHEN EXIT – WHEN GOTO GOTO

IF – THEN - ELSE DECLARE acct_balance NUMBER(11,2); acct CONSTANT NUMBER(4) := 3; debit_amt CONSTANT NUMBER(5,2) := ; BEGIN SELECT bal INTO acct_balance FROM accounts WHERE account_id = acct FOR UPDATE OF bal; IF acct_balance >= debit_amt THEN UPDATE accounts SET bal = bal - debit_amt WHERE account_id = acct; ELSE INSERT INTO temp VALUES (acct, acct_balance, ’Insufficient funds’); -- insert account, current balance, and message END IF; COMMIT; END;

WHILE DECLARE salary emp.sal%TYPE := 0; mgr_num emp.mgr%TYPE; last_name emp.ename%TYPE; starting_empno emp.empno%TYPE := 7499; BEGIN SELECT mgr INTO mgr_num FROM emp WHERE empno = starting_empno; WHILE salary <= 2500 LOOP SELECT sal, mgr, ename INTO salary, mgr_num, last_name FROM emp WHERE empno = mgr_num; END LOOP; INSERT INTO temp VALUES (NULL, salary, last_name); COMMIT; EXCEPTION WHEN NO_DATA_FOUND THEN INSERT INTO temp VALUES (NULL, NULL, ’Not found’); COMMIT; END;

MODULARITY Blocks Blocks Subprograms Subprograms Procedures Procedures Functions Functions Packages Packages

PROCEDURES PROCEDURE award_bonus (emp_id NUMBER) IS bonus REAL; comm_missing EXCEPTION; BEGIN -- executable part starts here SELECT comm * 0.15 INTO bonus FROM emp WHERE empno = emp_id; IF bonus IS NULL THEN RAISE comm_missing; ELSE UPDATE payroll SET pay = pay + bonus WHERE empno = emp_id; END IF; EXCEPTION -- exception-handling part starts here WHEN comm_missing THEN... END award_bonus;

PACKAGES CREATE PACKAGE emp_actions AS -- package specification PROCEDURE hire_employee (empno NUMBER, ename CHAR,...); PROCEDURE fire_employee (emp_id NUMBER); END emp_actions; CREATE PACKAGE BODY emp_actions AS -- package body PROCEDURE hire_employee (empno NUMBER, ename CHAR,...) IS BEGIN INSERT INTO emp VALUES (empno, ename,...); END hire_employee; PROCEDURE fire_employee (emp_id NUMBER) IS BEGIN DELETE FROM emp WHERE empno = emp_id; END fire_employee; END emp_actions;

DATA ABSTRACTION Collections Collections TABLES TABLES VARRAY VARRAY Records Records DECLARE TYPE TimeRec IS RECORD (hours SMALLINT, minutes SMALLINT); TYPE MeetingTyp IS RECORD ( date_held DATE, duration TimeRec, -- nested record location VARCHAR2(20), purpose VARCHAR2(50));

DATA ABSTRACTION Object types Object types Encapsulation Encapsulation Attributes and Methods Attributes and Methods Modular Modular Maintainable Maintainable Reusable Reusable

INFORMATION HIDING Algorithms Algorithms Hidden through Top - Down – Design Hidden through Top - Down – Design Accessed by interface specification Accessed by interface specification Data Structures Data Structures Hidden through data encapsulation Hidden through data encapsulation Accessed by utility subprograms Accessed by utility subprograms Can be made public Can be made public

ERROR HANDLING DECLARE... comm_missing EXCEPTION; -- declare exception BEGIN... IF commission IS NULL THEN RAISE comm_missing; -- raise exception END IF; bonus := (salary * 0.10) + (commission * 0.15); EXCEPTION WHEN comm_missing THEN process the exception

OBJECT TYPES CREATE TYPE Bank_Account AS OBJECT ( acct_number INTEGER(5), balance REAL, status VARCHAR2(10), MEMBER PROCEDURE open (amount IN REAL), MEMBER PROCEDURE verify_acct (num IN INTEGER), MEMBER PROCEDURE close (num IN INTEGER, amount OUT REAL), MEMBER PROCEDURE deposit (num IN INTEGER, amount IN REAL), MEMBER PROCEDURE withdraw (num IN INTEGER, amount IN REAL), MEMBER FUNCTION curr_bal (num IN INTEGER) RETURN REAL );

ADVANTAGES OF PL/SQL Support for SQL Support for SQL Support for Object - Oriented – Programming Support for Object - Oriented – Programming Better performance Better performance Higher productivity Higher productivity Full portability Full portability Tight integration with SQL Tight integration with SQL Tight security Tight security