mysql 数据操作 单表查询 having 过滤 练习

mysql> select post,group_concat(name),count(id) from employee group by post;
+-----------+-------------------------------------------------+-----------+
| post      | group_concat(name)                              | count(id) |
+-----------+-------------------------------------------------+-----------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野                |         5 |
| sale      | 格格,星星,丁丁,丫丫,歪歪                        |         5 |
| teacher   | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,alex   |         6 |
+-----------+-------------------------------------------------+-----------+
3 rows in set (0.00 sec)

mysql> select post,group_concat(name),count(id) from employee group by post having count(id) <2 ;
Empty set (0.05 sec)

mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post      | avg(salary)   |
+-----------+---------------+
| operation |  16800.026000 |
| teacher   | 175766.718333 |
+-----------+---------------+
2 rows in set (0.04 sec)

mysql> select post,avg(salary) from employee group by post having avg(salary) between 10000 and 20000;
+-----------+--------------+
| post      | avg(salary)  |
+-----------+--------------+
| operation | 16800.026000 |
+-----------+--------------+
1 row in set (0.00 sec)