mysql group by having 實例
注意:使用group by的時候,SELECT子句中的列名必須為分組列。 如下實例必須包括name列名,因為name是作為group by分組的條件。
實例:
我的數據庫中有一張員工工作記錄表,表中的數據庫如下:
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:現在我需要查找出每個員工工作了多少天,這時就需要用到group by語句:
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:我現在要查找工作天數大於一天的所有員工,這個時候就需要用到group by having語句
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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