mysql查询子句之三having条件查询(筛选)

having

作用：对查询的结果进行筛选操作
语法：having 条件 或者 having 聚合函数 条件
适用场合：一般跟在group by之后

mysql> select * from employee;
+-------+--------+--------+------+------------+----------+--------+
| empno | ename  | job    | mgr  | hiredate   | sal      | deptnu |
+-------+--------+--------+------+------------+----------+--------+
|  1004 | 猪八戒 | 经理   | 1009 | 2001-04-02 | 29750.00 |     20 |
|  1006 | 猴子   | 经理   | 1009 | 2011-05-01 | 28500.00 |     30 |
|  1007 | 张飞   | 经理   | 1009 | 2011-09-01 | 24500.00 |     10 |
|  1008 | 诸葛亮 | 分析师 | 1004 | 2017-04-19 | 30000.00 |     20 |
|  1013 | 林俊杰 | 分析师 | 1004 | 2011-12-03 | 30000.00 |     20 |
|  1002 | 牛魔王 | 销售员 | 1006 | 2018-02-20 | 16000.00 |     30 |
|  1003 | 程咬金 | 销售员 | 1006 | 2017-02-22 | 12500.00 |     30 |
|  1005 | 后裔   | 销售员 | 1006 | 2011-09-28 | 12500.00 |     30 |
|  1010 | 韩信   | 销售员 | 1006 | 2018-09-08 | 15000.00 |     30 |
|  1012 | 安琪拉 | 文员   | 1006 | 2011-12-03 | 9500.00  |     30 |
|  1014 | 甄姬   | 文员   | 1007 | 2019-01-23 | 7500.00  |     10 |
|  1011 | 妲己   | 文员   | 1008 | 2018-05-23 | 11000.00 |     20 |
|  1001 | 小乔   | 文员   | 1013 | 2018-12-17 | 8000.00  |     20 |
+-------+--------+--------+------+------------+----------+--------+
13 rows in set (0.03 sec)

mysql> select deptnu,count(*) from employee group by deptnu;
+--------+----------+
| deptnu | count(*) |
+--------+----------+
|     10 |        2 |
|     20 |        5 |
|     30 |        6 |
+--------+----------+
3 rows in set (0.03 sec)

mysql> select deptnu,count(*) from employee group by deptnu having count(*)>2;
+--------+----------+
| deptnu | count(*) |
+--------+----------+
|     20 |        5 |
|     30 |        6 |
+--------+----------+
2 rows in set (0.04 sec)

mysql> select deptnu,job,count(*) from employee group by deptnu,job ;
+--------+--------+----------+
| deptnu | job    | count(*) |
+--------+--------+----------+
|     10 | 文员   |        1 |
|     10 | 经理   |        1 |
|     20 | 分析师 |        2 |
|     20 | 文员   |        2 |
|     20 | 经理   |        1 |
|     30 | 文员   |        1 |
|     30 | 经理   |        1 |
|     30 | 销售员 |        4 |
+--------+--------+----------+
8 rows in set (0.03 sec)

mysql> select deptnu,job,count(*) as num from employee group by deptnu,job having num>=2;
+--------+--------+-----+
| deptnu | job    | num |
+--------+--------+-----+
|     20 | 分析师 |   2 |
|     20 | 文员   |   2 |
|     30 | 销售员 |   4 |
+--------+--------+-----+
3 rows in set (0.02 sec)

mysql> select deptnu,job,count(*) as num from employee group by deptnu,job having job='文员' and num>=2;
+--------+------+-----+
| deptnu | job  | num |
+--------+------+-----+
|     20 | 文员 |   2 |
+--------+------+-----+
1 row in set (0.03 sec)