1.資料庫表

DROP TABLE IF EXISTS emp;
CREATE TABLE emp (
  empno decimal(4,0) NOT NULL,
  ename varchar(10) DEFAULT NULL,
  job varchar(9) DEFAULT NULL,
  mgr decimal(4,0) DEFAULT NULL,
  hiredate datetime DEFAULT NULL,
  sal decimal(7,2) DEFAULT NULL,
  comm decimal(7,2) DEFAULT NULL,
  deptno decimal(2,0) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
 

2.插入的資料

INSERT INTO emp VALUES ('7369', 'SMITH', 'CLERK', '7902', '1980-12-17 00:00:00', '800.00', null, '20');
INSERT INTO emp VALUES ('7499', 'ALLEN', 'SALESMAN', '7698', '1981-02-20 00:00:00', '1600.00', '300.00', '30');
INSERT INTO emp VALUES ('7521', 'WARD', 'SALESMAN', '7698', '1981-02-22 00:00:00', '1250.00', '500.00', '30');
INSERT INTO emp VALUES ('7566', 'JONES', 'MANAGER', '7839', '1981-04-02 00:00:00', '2975.00', null, '20');
INSERT INTO emp VALUES ('7654', 'MARTIN', 'SALESMAN', '7698', '1981-09-28 00:00:00', '1250.00', '1400.00', '30');
INSERT INTO emp VALUES ('7698', 'BLAKE', 'MANAGER', '7839', '1981-05-01 00:00:00', '2850.00', null, '30');
INSERT INTO emp VALUES ('7782', 'CLARK', 'MANAGER', '7839', '1981-06-09 00:00:00', '2450.00', null, '10');
INSERT INTO emp VALUES ('7788', 'SCOTT', 'ANALYST', '7566', '1982-12-09 00:00:00', '3000.00', null, '20');
INSERT INTO emp VALUES ('7839', 'KING', 'PRESIDENT', null, '1981-11-17 00:00:00', '5000.00', null, '10');
INSERT INTO emp VALUES ('7844', 'TURNER', 'SALESMAN', '7698', '1981-09-08 00:00:00', '1500.00', '0.00', '30');
INSERT INTO emp VALUES ('7876', 'ADAMS', 'CLERK', '7788', '1983-01-12 00:00:00', '1100.00', null, '20');
INSERT INTO emp VALUES ('7900', 'JAMES', 'CLERK', '7698', '1981-12-03 00:00:00', '950.00', null, '30');
INSERT INTO emp VALUES ('7902', 'FORD', 'ANALYST', '7566', '1981-12-03 00:00:00', '3000.00', null, '20');
INSERT INTO emp VALUES ('7934', 'MILLER', 'CLERK', '7782', '1982-01-23 00:00:00', '1300.00', null, '10');
 

3.查詢語句

select * from emp as a where 4> (select count(*) from emp where deptno = a.deptno and sal < a.sal  )  order by a.deptno ,a.sal

4.大體思路

解析SQL：

4>...

目的是獲取前三條資料，可以多次修改

emp where deptno = a.deptno

目的是確定分組欄位

sal < a.sal

排序條件