mysql group by having 实例代码

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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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