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：
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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：
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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
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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) |
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