PL/SQL, Embedded SQL. Lecture #14 Autumn, Fall, 2001, LRX

Transcription

1 PL/SQL, Embedded SQL Lecture #14 Autumn, 2001 Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 402

2 PL/SQL Found ony in the Orace SQL processor (sqpus). A compromise between competey procedura programming and SQL's very high-eve, but imited statements. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 403

3 PL/SQL (II) Aows oca variabes, oops, procedures, examination of reations one tupe at a time. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 404

4 PL/SQL (III) Rough form: DECLARE decarations BEGIN executabe statements END;. run; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 405

5 PL/SQL (IV) DECLARE portion is optiona. Dot and run are needed to end the statement and execute it. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 406

6 Simpest Form: Sequence of Modifications Likes(drinker, beer) BEGIN INSERT INTO Likes VALUES('Say', 'Bud'); DELETE FROM Likes WHERE drinker = 'Fred' END;. run; AND beer = 'Mier'; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 407

7 Procedures Stored database objects that use a PL/SQL statement in their body. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 408

8 Procedures (II) Form of decaration: CREATE OR REPLACE PROCEDURE <name>(<argist>) AS decarations BEGIN <PL/SQL statements> END;. run; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 409

9 Procedures (III) Argument ist has name-mode-type tripes.»mode: IN, OUT, or INOUT, as in ODL.»Types: standard SQL + generic types ike NUMBER = any integer or rea type. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 410

10 Procedures (IV)»Since types in procedures must match their types in the DB schema, you shoud generay use an expression of the form reation.attribute%type to capture the type correcty. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 411

11 Exampe A procedure to take a beer and price and add it to Joe's menu. Ses(bar, beer, price) Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 412

12 Exampe (II) CREATE PROCEDURE joemenu( b IN Ses.beer%TYPE, p IN Ses.price%TYPE ) AS BEGIN INSERT INTO Ses VALUES('Joe''s Bar', b, p); END;. run; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 413

13 Exampe (III) Note "run" ony stores the procedure; it doesn't execute the procedure. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 414

14 Invoking Procedures A procedure ca may appear in the body of a PL/SQL statement. Exampe: BEGIN joemenu('bud', 2.50); joemenu('moosedroo', 5.00); END;. run; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 415

15 Assignment Assign expressions to decared variabes with :=. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 416

16 Branches IF <condition> THEN <statement(s)> ELSE <statement(s)> END IF; But in nests, use ELSIF in pace of ELSE IF. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 417

17 Loops LOOP... EXIT WHEN <condition>... END LOOP; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 418

18 Cursors Decare by: CURSOR <name> IS seect-from-where statement Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 419

19 Cursors (II) Cursor gets each tupe from the reation produced by the seect-from-where, in turn, using a fetch statement in a oop.»fetch statement: FETCH <cursor name> INTO variabe ist; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 420

20 Cursors (III) Break the oop by a statement of the form: EXIT WHEN <cursor name>%notfound;»true when there are no more tupes to get. Open and cose the cursor with OPEN and CLOSE. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 421

21 Exampe A procedure that examines the menu for Joe's Bar and raises by $1.00 a prices that are ess than $3.00. Ses(bar, beer, price) Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 422

22 Exampe (II) This simpe price-change agorithm can be impemented by a singe UPDATE statement, but more compicated price changes coud not. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 423

23 Exampe (III) CREATE PROCEDURE joegouge() AS thebeer Ses.beer%TYPE; theprice Ses.price%TYPE; CURSOR c IS SELECT beer, price FROM Ses WHERE bar = 'Joe''s bar'; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 424

24 Exampe (III) BEGIN OPEN c; LOOP FETCH c INTO thebeer, theprice; EXIT WHEN c%notfound; IF theprice < 3.00 THEN UDPATE Ses SET price = theprice WHERE bar = 'Joe''s Bar' AND beer = thebeer; END IF; END LOOP; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 425

25 Exampe (IV) CLOSE c; END;. run Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 426

26 Singe-Row Seect Seect-from-where in PL/SQL must have an INTO cause isting variabes into which a tupe can be paced. It is an error if the seect-from-where returns more than one tupe; you shoud have used a cursor. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 427

27 Exampe Find the price Joe charges for Bud (and drop it on the foor). Ses(bar, beer, price) DECLARE p Ses.price%TYPE; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 428

28 Exampe (II) BEGIN SELECT price INTO p FROM Ses WHERE bar = 'Joe''s Bar' AND beer = 'Bud'; END;. run Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 429

29 SQL2 Embedded SQL Add to a conventiona programming anguage (C in our exampes) certain statements that represent SQL operations. Each embedded SQL statement introduced with EXEC SQL. Preprocessor converts C + SQL to pure C.» SQL statements become procedure cas. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 430

30 Shared Variabes A specia pace for C decarations of variabes that are accessibe to both SQL and C. Bracketed by EXEC SQL BEGIN/END DECLARE SECTION; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 431

31 Shared Variabes (II) In Orace Pro/C (not C++) the "brackets" are optiona. In C, variabes used normay; in SQL, they must be preceded by a coon. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 432

32 Exampe Find the price for a given beer at a given bar. Ses(bar, beer, price) Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 433

33 Exampe (II) EXEC SQL BEGIN DECLARE SECTION; char thebar[21], thebeer[21]; foat theprice; EXEC SQL END DECLARE SECTION;... /* assign to thebar and thebeer */... EXEC SQL SELECT price INTO :theprice FROM Ses WHERE beer = :thebeer AND bar = :thebar;... Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 434

34 Cursors Simiar to PL/SQL cursors, with some syntactic differences. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 435

35 Exampe Print Joe's menu. Ses(bar, beer, price) Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 436

36 Exampe (II) EXEC SQL BEGIN DECLARE SECTION; char thebeer[21]; foat theprice; EXEC SQL END DECLARE SECTION; EXEC SQL DECLARE c CURSOR FOR SELECT beer, price FROM Ses WHERE bar = 'Joe''s Bar'; EXEC SQL OPEN CURSOR c; whie(1) { EXEC SQL FETCH c INTO :thebeer, :theprice; if(not FOUND) break; /* format and print beer and price */ } EXEC SQL CLOSE CURSOR c; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 437

37 Orace Vs. SQL2 Features SQL2 expects FROM in fetch-statement. SQL2 defines an array of characters SQLSTATE that is set every time the system is caed.» Errors are signaed there. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 438

38 Orace Vs. SQL2 Features (II)» A faiure for a cursor to find any more tupes is signaed there.» However, Orace provides us with a header fie sqca.h that decares a communication area and defines macros to access it.» In particuar, NOT FOUND is a macro that says "the no-tupe-found signa was set." Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 439

39 Dynamic SQL Motivation:» Embedded SQL is fine for fixed appications, e.g., a program that is used by a saes cerk to book an airine seat.» It fais if you try to write a program ike sqpus, because you have compied the code for sqpus before you see the SQL statements typed in response to the SQL> prompt. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 440

40 Dynamic SQL (II)» Two specia statements of embedded SQL: PREPARE turns a character string into an SQL query. EXECUTE executes that query. Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 441

41 Exampe: Sqpus Sketch EXEC SQL BEGIN DECLARE SECTION; char query[max_query_length]; EXEC SQL END DECLARE SECTION; /* issue SQL> prompt */ /* read user's text into array query */ EXEC SQL PREPARE q FROM :query; EXEC SQL EXECUTE q; /* go back to reissue prompt */ Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 442

42 Exampe: Sqpus Sketch (II) Once prepared, a query can be executed many times. Aternativey, PREPARE and EXECUTE can be combined into: EXEC SQL EXECUTE IMMEDIATE :query; Fa, 2001, LRX #14 PL/SQL,Embedded SQL HUST,Wuhan,China 443