Database Application Development

Transcription

1 Database Application Development Chapter 6 PSM (Stored Procedures) 1

2 Stored Procedures What is a stored procedure: SQL allows you to define procedures and functions and store in the DB server Program executed through single SQL statement Executed in process space by the database server Advantages: Can encapsulate application logic while staying close to the data (usually implies efficiency) Reuse of application logic by different users Avoid tuple-at-a-time return of records through cursors (as would be done by JDBC) 2

3 SQL/PSM Declare a stored procedure: CREATE PROCEDURE name(p1, p2,, pn) local variable declarations procedure code for body; Declare a function: CREATE FUNCTION name (p1,, pn) RETURNS sqldatatype local variable declarations function code; 3

4 Stored Procedures: Examples CREATE PROCEDURE ShowNumReservations SELECT S.sid, S.sname, COUNT(*) FROM Sailors S, Reserves R WHERE S.sid = R.sid GROUP BY S.sid, S.sname; 4

5 Stored Procedures: Examples Stored procedures can have parameters: <name> <mode> <type> <mode> is one of {IN, OUT, INOUT} eg: IN val1 int CREATE PROCEDURE IncreaseRating( IN sailor_sid INTEGER, IN increase INTEGER) UPDATE Sailors SET rating = rating + increase WHERE sid = sailor_sid; 5

6 Stored Procedures: Examples Stored procedure do not have to be in SQL: CREATE PROCEDURE TopSailors( IN num INTEGER) LANGUAGE JAVA EXTERNAL NAME file:///c:/storedprocs/rank.jar 6

7 Example: Procedure in PSM CREATE PROCEDURE testprocedure BEGIN INSERT INTO Student VALUES (5, Joe ); END; Oracle s version of PSM : CREATE PROCEDURE testprocedure IS BEGIN INSERT INTO Student VALUES (5, Joe ); END;. run; NOTE: mysql later versions have initial support. 7

8 Also You can drop procedure by DROP PROCEDURE <procedurename> In PL/SQL, you can replace procedure by CREATE OR REPLACE PROCEDURE <procedurename> 8

9 Calling Stored Procedures Calling Procedures call <procedurename> [(<paramlist>)]; Embedded SQL: EXEC SQL BEGIN DECLARE SECTION Int sid; Int rating; EXEC SQL END DECLARE SECTION // now increase rating of this sailor EXEC CALL IncreaseRating(:sid,:rating); 9

10 Stored Procedures : Persistent Stored Modules (PSM) 10

11 SQL/PSM Most DBMSs allow users to write stored procedures in a simple general-purpose language (close to SQL) SQL/PSM standard is a representative of vendor-specific languages. Oracle supports a slightly different version of PSM called PL/SQL 11

12 Local Declarations CREATE PROCEDURE testprocedure (num IN int, name IN varchar) IS BEGIN INSERT INTO Student VALUES (num, name); END; 12

13 Local Declarations CREATE PROCEDURE testprocedure (num IN int, name IN varchar) IS num1 int; BEGIN END; num1 := 10; -- local variable INSERT INTO Student VALUES (num1, name); 13

14 Other PSM features Assignment statements: PL/SQL <varname> := <expression> 14

15 Control Structures: IF THEN ELSE IF <condition> THEN <statementlist> ELSIF <condition> THEN <statementlist> ELSIF ELSE <statementlist> END IF; 15

16 Loops LOOP <statementlist> END LOOP; To exit from a loop use EXIT; 16

17 Loops: Example CREATE PROCEDURE testprocedure (num IN int, name IN varchar) IS num1 int; BEGIN END; num1 := 10; LOOP END LOOP; INSERT INTO Student VALUES (num1, name); num1 := num1 + 1; IF (num1 > 15) THEN EXIT; END IF; 17

18 FOR Loops FOR i in [REVERSE] <lowerbound>.. <upperbound> LOOP <statementlist> END LOOP Example: FOR i in LOOP INSERT INTO Student (snumber) values (10 + i); END LOOP; 18

19 WHILE LOOPS WHILE <condition> LOOP <statementlist> END LOOP; 19

20 Functions CREATE FUNCTION <functionname> [(<paramlist>)] RETURNS type AS <localdeclarations> BEGIN <functionbody>; END; You can call a function as part of an SQL expression Drop a function: drop function <functionname> 20

21 Functions: Example CREATE FUNCTION testfunction RETURN int AS num1 int; BEGIN SELECT MAX (snumber) INTO num1 FROM Student; RETURN num1; END; SELECT * from Student where snumber = testfunction (); 21

22 SQL/PSM Example CREATE FUNCTION rate Sailor (IN sailorid INTEGER) RETURNS INTEGER DECLARE rating INTEGER; DECLARE numres INTEGER; BEGIN SET numres = (SELECT COUNT(*) FROM Reserves R WHERE R.sid = sailorid); IF (numres > 10) THEN rating =1; ELSE rating = 0; END IF; RETURN rating; END 22

23 Other Info Re Oracle : Oracle stores procedures and functions in catalog as relational tables: Check user_procedures Check user_functions You may run queries against them such as: describe user_procedures; select object_name from user_procedures; 23

24 Summary : Stored Procedures Stored procedures execute application logic directly at the server SQL/PSM standard for writing stored procedural logic: Used stand-alone on explicit call Used functions in WHERE clause of SQL statement Used in body of triggers 24