实例：
我的数据库中有一张员工工作记录表，表中的数据库如下：
mysql> SELECT * FROM employee_tbl;
+------+------+------------+--------------------+
| id | name | work_date | daily_typing_pages |
+------+------+------------+--------------------+
| 1 | John | 2007-01-24 | 250 |
| 2 | Ram | 2007-05-27 | 220 |
| 3 | Jack | 2007-05-06 | 170 |
| 3 | Jack | 2007-04-06 | 100 |
| 4 | Jill | 2007-04-06 | 220 |
| 5 | Zara | 2007-06-06 | 300 |
| 5 | Zara | 2007-02-06 | 350 |
+------+------+------------+--------------------+
7 rows in set (0.00 sec)
需求一：现在我需要查找出每个员工工作了多少天，这时就需要用到group by语句：
mysql> SELECT name, COUNT(*)
-> FROM employee_tbl
-> GROUP BY name;
+------+----------+
| name | COUNT(*) |
+------+----------+
| Jack | 2 |
| Jill | 1 |
| John | 1 |
| Ram | 1 |
| Zara | 2 |
+------+----------+
5 rows in set (0.04 sec)
需求二：我现在要查找工作天数大于一天的所有员工，这个时候就需要用到group by having语句
mysql> SELECT name, COUNT(*)
-> FROM employee_tbl
-> GROUP BY name having COUNT(*)>1 ;
+------+----------+
| name | COUNT(*) |
+------+----------+
| Jack | 2 |
| Zara | 2 |
+------+----------+
2 rows in set (0.04 sec)声明：本文内容由网友自发贡献，版权归原作者所有，本站不承担相应法律责任。如您发现有涉嫌抄袭侵权的内容，请联系admin@php.cn核实处理。
