exists 的简单介绍

准备数据：

 1 CREATE TABLE Books(
 2     BookID number,
 3     BookTitle VARCHAR2(20) NOT NULL,
 4     Copyright varchar2(20)
 5 )
 6 INSERT INTO Books VALUES (12786, 'Java',1934);
 7 INSERT INTO Books VALUES (13331, 'MySQL',1919);
 8  INSERT INTO Books VALUES (14356, 'PHP',1966);
 9  INSERT INTO Books VALUES (15729, 'PERL',1932);
10  INSERT INTO Books VALUES (16284, 'Oracle',1996);
11  INSERT INTO Books VALUES (17695, 'Pl/SQL',1980);
12  INSERT INTO Books VALUES (19264, 'JavaScript',1992);
13  INSERT INTO Books VALUES (19354, 'www.manongjc.com',1993);
14 
15 CREATE TABLE AuthorBook(
16     AuthID NUMBER,
17     BookID NUMBER
18     )
19 
20 INSERT INTO AuthorBook VALUES (1006, 14356);
21 INSERT INTO AuthorBook VALUES (1008, 15729);
22 INSERT INTO AuthorBook VALUES (1009, 12786);
23 INSERT INTO AuthorBook VALUES (1010, 17695);
24 INSERT INTO AuthorBook VALUES (1011, 15729);
25 INSERT INTO AuthorBook VALUES (1012, 19264);
26 INSERT INTO AuthorBook VALUES (1012, 19354);
27 INSERT INTO AuthorBook VALUES (1014, 16284);

BOOKS表：

AUTHORBOOK表：

查询B表ID在A表中的数据

 1 select * from BOOKS B 2 WHERE EXISTS (SELECT * FROM AUTHORBOOK A WHERE A.BOOKID=B.BOOKID) 

EXISTS后面表示的只有两个值。就是“真”或者“假”。 NOT EXISTS 与EXISTS相反。

 

posted @ 2017-09-20 10:31  陆伟  阅读(328)  评论(0)  编辑  收藏  举报