DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`number` int(11) DEFAULT NULL,
`name` varchar(255) DEFAULT NULL,
`role` varchar(255) DEFAULT NULL,
PRIMARY KEY (`id`)
) ；
INSERT INTO `emp` VALUES (1,1001,'a','read');
INSERT INTO `emp` VALUES (2,1001,'a','write');
INSERT INTO `emp` VALUES (3,1001,'a','copy');
INSERT INTO `emp` VALUES (4,1002,'b','read');
INSERT INTO `emp` VALUES (5,1002,'b','write');
INSERT INTO `emp` VALUES (7,1003,'c','listen');
INSERT INTO `emp` VALUES (8,1003,'c','read');
INSERT INTO `emp` VALUES (9,1004,'d','read');
INSERT INTO `emp` VALUES (10,1004,'d','write');
INSERT INTO `emp` VALUES (11,1005,'e','read');
INSERT INTO `emp` VALUES (12,1005,'e','write');
有兩種方式可以查詢（Mysql）
1.select ep.number,ep.role from emp ep,
(select role,number from emp where number=1002) e
where e.role= ep.role and e.number!= ep.number
group by number
having count(*)=(select count(number) from emp where number=1002 )；
在這里having 后的 要寫count(*) 而不是count(number) 否則會報錯
結果:
number count(*)
1001 2
1004 2
1005 2
2.select number,count(*) from emp
where role in (select role from emp where number=1002)
and number !=1002
group by number
having count(number) =(select count(number) from emp where number=1002);
number count(*)
1001 2
1004 2
1005 2