mysql having实例_mysql group by having 实例代码

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：

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)

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