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mysql group by having 實(shí)例MYSQL實(shí)例
注意：使用group by的時(shí)候,SELECT子句中的列名必須為分組列. 如下實(shí)例必須包括name列名,因?yàn)閚ame是作為group by分組的條件.MYSQL實(shí)例
實(shí)例：MYSQL實(shí)例
我的數(shù)據(jù)庫(kù)中有一張員工工作記錄表,表中的數(shù)據(jù)庫(kù)如下：MYSQL實(shí)例
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(xiàn)在我需要查找出每個(gè)員工工作了多少天,這時(shí)就需要用到group by語(yǔ)句：MYSQL實(shí)例
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(xiàn)在要查找工作天數(shù)大于一天的所有員工,這個(gè)時(shí)候就需要用到group by having語(yǔ)句MYSQL實(shí)例
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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