mysql group by having 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。
實(shí)例:
我的數(shù)據(jù)庫中有一張員工工作記錄表,表中的數(shù)據(jù)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(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(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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