使用group by字句对列进行分组
使用having字句对分别组后的结果进行过滤
#演示group by + having的使用 #部门表 CREATE TABLE dept( deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, dname VARCHAR(20) NOT NULL DEFAULT "", loc VARCHAR(13) NOT NULL DEFAULT "" ); INSERT INTO dept VALUES(10, 'ACCOUNTING', 'NEW YORK'), (20, 'RESEARCH', 'DALLAS'), (30, 'SALES', 'CHICAGO'), (40, 'OPERATIONS', 'BOSTON'); SELECT * FROM dept; #雇员表 CREATE TABLE emp (empno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, /*编号*/ ename VARCHAR(20) NOT NULL DEFAULT "", /*名字*/ job VARCHAR(9) NOT NULL DEFAULT "",/*工作*/ mgr MEDIUMINT UNSIGNED ,/*上级编号*/ hiredate DATE NOT NULL,/*入职时间*/ sal DECIMAL(7,2) NOT NULL,/*薪水*/ comm DECIMAL(7,2) ,/*红利*/ deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 /*部门编号*/ ); #添加测试数据 INSERT INTO emp VALUES(7369, 'SMITH', 'CLERK', 7902, '1990-12-17', 800.00,NULL , 20), (7499, 'ALLEN', 'SALESMAN', 7698, '1991-2-20', 1600.00, 300.00, 30), (7521, 'WARD', 'SALESMAN', 7698, '1991-2-22', 1250.00, 500.00, 30), (7566, 'JONES', 'MANAGER', 7839, '1991-4-2', 2975.00,NULL,20), (7654, 'MARTIN', 'SALESMAN', 7698, '1991-9-28',1250.00,1400.00,30), (7698, 'BLAKE','MANAGER', 7839,'1991-5-1', 2850.00,NULL,30), (7782, 'CLARK','MANAGER', 7839, '1991-6-9',2450.00,NULL,10), (7788, 'SCOTT','ANALYST',7566, '1997-4-19',3000.00,NULL,20), (7839, 'KING','PRESIDENT',NULL,'1991-11-17',5000.00,NULL,10), (7844, 'TURNER', 'SALESMAN',7698, '1991-9-8', 1500.00, NULL,30), (7900, 'JAMES','CLERK',7698, '1991-12-3',950.00,NULL,30), (7902, 'FORD', 'ANALYST',7566,'1991-12-3',3000.00, NULL,20), (7934,'MILLER','CLERK',7782,'1992-1-23', 1300.00, NULL,10); SELECT * FROM emp; #工资级别表 CREATE TABLE salgrade ( grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, -- 工资级别 losal DECIMAL(17,2) NOT NULL, -- 该级别最低工资 hisal DECIMAL(17,2) NOT NULL -- 该级别最高工资 ); #添加数据 INSERT INTO salgrade VALUES (1,700,1200); INSERT INTO salgrade VALUES (2,1201,1400); INSERT INTO salgrade VALUES (3,1401,2000); INSERT INTO salgrade VALUES (4,2001,3000); INSERT INTO salgrade VALUES (5,3001,9999); SELECT * FROM salgrade; #显示每个部门的平均工资和最高工资 SELECT AVG(sal),MAX(sal),deptno FROM emp GROUP BY deptno; #显示每个部门的每种岗位的平均工资和最低工资 SELECT AVG(sal),MIN(sal),deptno , job FROM emp GROUP BY deptno ,job; #显示平均工资低于2000的部门号和它的平均工资 SELECT AVG(sal),deptno FROM emp GROUP BY deptno HAVING AVG(sal) < 2000;
