SQL3 Objects. Lecture #20 Autumn, Fall, 2001, LRX

Transcription

1 SQL3 Objects Lecture #20 Autumn, 2001 #20 SQL3 Objects HUST,Wuhan,China 588

2 Objects in SQL3 OQL extends C++ with database concepts, whie SQL3 extends SQL with OO concepts. #20 SQL3 Objects HUST,Wuhan,China 589

3 Objects in SQL3 (II) Uman's persona opinion: the reation is so fundamenta to data manipuation that retaining it as the core, as SQL3 does, is "right." Systems using the SQL3 phiosophy are caed object-reationa. #20 SQL3 Objects HUST,Wuhan,China 590

4 Objects in SQL3 (III)» A the major reationa vendors have something of this kind, aowing any cass to become the type of a coumn. Informix Data Bades Orace Cartridges Sybase Pug-Ins IBM/DB2 Extenders #20 SQL3 Objects HUST,Wuhan,China 591

5 Two Leves of SQL3 Objects 1. For tupes of reations = "row types." 2. For coumns of reations = "types."» But row types can aso be used as coumn types. #20 SQL3 Objects HUST,Wuhan,China 592

6 References Row types can have references. If T is a row type, then REF(T) is the type of a reference to a T object. Unike OO systems, refs are vaues that can be seen by queries. #20 SQL3 Objects HUST,Wuhan,China 593

7 Exampe of Row Types CREATE ROW TYPE BarType ( name CHAR(20) UNIQUE, addr CHAR(20) ); CREATE ROW TYPE BeerType ( name CHAR(20) UNIQUE, manf CHAR(20) ); #20 SQL3 Objects HUST,Wuhan,China 594

8 Exampe of Row Types (II) CREATE ROW TYPE MenuType ( bar REF(BarType), beer REF(BeerType), price FLOAT ); #20 SQL3 Objects HUST,Wuhan,China 595

9 Creating Tabes Row-type decarations do not create tabes.» They are used in pace of eement ists in CREATE TABLE statements. Exampe» CREATE TABLE Bars OF TYPE BarType» CREATE TABLE Beers OF TYPE BeerType» CREATE TABLE Ses OF TYPE MenuType #20 SQL3 Objects HUST,Wuhan,China 596

10 Dereferencing A B = the B attribute of the object referred to by reference A. Exampe» Find the beers served by Joe. SELECT beer -> name FROM Ses WHERE bar -> name = 'Joe''s Bar'; #20 SQL3 Objects HUST,Wuhan,China 597

11 OID's as Vaues A row type can have a reference to itsef.» Serves as the OID for tupes of that type. Exampe CREATE ROW TYPE BarType ( name CHAR(20), addr CHAR(20), barid REF(BarType) ); CREATE TABLE Bars OF TYPE BarType VALUES FOR barid ARE SYSTEM GENERATED #20 SQL3 Objects HUST,Wuhan,China 598

12 OID's as Vaues (II) VALUES... cause forces the barid of each tupe to refer to the tupe itsef. Name addr barid Joe's Mape St. #20 SQL3 Objects HUST,Wuhan,China 599

13 Exampe: Using References as Vaues Find the menu at Joe's. SELECT Ses.beer->name, Ses.price FROM Bars, Ses WHERE Bars.name = 'Joe''s Bar' AND Bars.barID = Ses.bar; #20 SQL3 Objects HUST,Wuhan,China 600

14 ADT's in SQL3 Aows a coumn of a reation to have a type that is a "cass," incuding methods. Intended appication: data that doesn't fit reationa mode we, e.g., ocations, signas, images, etc. The type itsef is usuay a muti-attribute tupe. #20 SQL3 Objects HUST,Wuhan,China 601

15 ADT's in SQL3 (II) Type decaration: CREATE TYPE <name> ( attributes method decarations or definitions ); Methods defined in a PL/SQL-ike anguage. #20 SQL3 Objects HUST,Wuhan,China 602

16 Exampe CREATE TYPE BeerADT ( name CHAR(20), manf CHAR(20), FUNCTION newbeer( :n CHAR(20), :m CHAR(20)) RETURNS BeerADT; :b BeerADT; /* oca dec. */ BEGIN :b := BeerADT(); /* buit-in constructor */ :b.name := :n; :b.manf := :m; RETURN :b; END; FUNCTION getminprice(:b BeerADT) RETURNS FLOAT; ); #20 SQL3 Objects HUST,Wuhan,China 603

17 Exampe (II) getminprice is decaration ony; newbeer is definition. getminprice must be defined somewhere where reation Ses is avaiabe. #20 SQL3 Objects HUST,Wuhan,China 604

18 Exampe (III) FUNCTION getminprice(:b BeerADT) RETURNS FLOAT; :p FLOAT; BEGIN SELECT MIN(price) INTO :p FROM Ses WHERE beer->name = :b.name; RETURN :p; END; #20 SQL3 Objects HUST,Wuhan,China 605

19 Buit-In Comparison Functions We can define for each ADT two functions EQUAL and LESSTHAN that aow vaues of this ADT to participate in WHERE causes invoving =, <=, etc. #20 SQL3 Objects HUST,Wuhan,China 606

20 Exampe: A "Point" ADT CREATE TYPE Point ( x FLOAT, y FLOAT, FUNCTION EQUALS( :p Point, :q Point ) RETURNS BOOLEAN; BEGIN IF :p.x = :q.x AND :p.y = :q.y THEN RETURN TRUE ELSE RETURN FALSE; END; #20 SQL3 Objects HUST,Wuhan,China 607

21 Exampe: A "Point" ADT (II) FUNCTION LESSTHAN( :p Point, :q Point ) RETURNS BOOLEAN; BEGIN IF :p.x > :q.x THEN RETURN FALSE ELSIF :p.x < :q.x THEN IF :p.y <= :q.y THEN RETURN TRUE ELSE RETURN FALSE ELSE /* :p.x = :q.x IF :p.y < :q.y THEN RETURN TRUE ELSE RETURN FALSE END; ); #20 SQL3 Objects HUST,Wuhan,China 608

22 Using the Comparison Functions Here is a query that computes the ower convex hu of a set of points. Assumes MyPoints(p) is a reation with a singe coumn p of type Point.» SELECT p FROM MyPoints WHERE NOT p > ANY MyPoints; #20 SQL3 Objects HUST,Wuhan,China 609

23 Using the Comparison Functions (II) #20 SQL3 Objects HUST,Wuhan,China 610