Question

我有下表;

  user  | column2    |
--------+------------+
 tom    |   Created  |
 test   |   Created  |
 fred   |   Removed  |
 tom    |   Removed  |
 fred   |   Created  |
 holly  |   Created  |
 test   |   Modified |

我希望查询该表以返回具有CREATED且没有具有REMOVED值的用户的用户。此外，具有MODIFIED的用户可以显示，但不能显示具有MODIFIED值的行。

结果应该是：

 user  | column2    |
-------+------------+
 test   |   Created |
 Holly  |   Created |

我只使用WHERE子句，还有另一种方法可以实现吗？

非常感谢任何给出的建议

Answer 1

使用NOT EXISTS：

SELECT user, column2
FROM mytable AS t1
WHERE column2 = 'Created' AND 
      NOT EXISTS (SELECT 1
                  FROM mytable AS t2 
                  WHERE t1.user = t2.user AND t2.column2 = 'Removed')

Answer 2

您可以使用LEFT JOIN

来完成

SELECT t.user,t.column2
FROM YourTable t
LEFT OUTER JOIN YourTable s
 ON(t.user = s.user and s.column2 = 'Removed')
WHERE s.user is null
     and t.column2 ='Created'

Answer 3

另一种方法，做一个GROUP BY。让HAVING子句检查用户的最小值是否已创建。

select user, min(column2)
from tablename
group by user
having min(column2) = 'Created'
   and max(column2) < 'Removed'

SQL - SELECT DISTINCT用户，当它们与COLUMN1 VALUEA匹配但没有COLUMN1 VALUEB时

3 个答案: