mysql group by having 实例
注意:使用group by的时候,SELECT子句中的列名必须为分组列。 如下实例必须包括name列名,因为name是作为group by分组的条件。
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:
1
2
3
4
5
6
7
8
9
10
11
12
13
|
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:
1
2
3
4
5
6
7
8
9
10
11
12
13
|
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
1
2
3
4
5
6
7
8
9
10
|
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)
|
感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!