按特定值除外的组

Question

我正在尝试创建一个(sqlite)查询,该查询将执行GROUP BY,但不会将值为'unknown'的任何内容组合在一起.例如,我有表:

id |   name  | parent_id | school_id |
 1 | john    |   1       |    1      |
 2 | john    |   1       |    1      |
 3 | john    |   1       |    1      |
 4 | nick    |   2       |    2      |
 5 | nick    |   2       |    2      |
 6 | nick    |   3       |    3      |
 7 | bob     |   4       |    4      |
 8 | unknown |   5       |    5      |
 9 | unknown |   5       |    5      |
 10| unknown |   5       |    5      |

通过'GROUP BY name,parent_id,school_id'的正确查询,我需要返回以下行:

id |   name  | parent_id | school_id |
 1 | john    |   1       |    1      |
 3 | nick    |   2       |    2      |
 4 | nick    |   3       |    3      |
 5 | bob     |   4       |    4      |
 6 | unknown |   5       |    5      |
 7 | unknown |   5       |    5      |
 8 | unknown |   5       |    5      |

任何帮助将不胜感激.谢谢!

Answer 1

您不能轻易地使用一个语句执行此操作,但您可以UNION使用两个语句的结果

• GROUP所有的名单,但 unknown
• 添加(UNION)所有列表unknown

SQL语句

SELECT MIN(id), name, parent_id, school_id
FROM   YourTable
WHERE  name <> 'unknown'
GROUP BY
       name, parent_id, school_id
UNION ALL
SELECT id, name, parent_id, school_id
FROM   YourTable
WHERE  name = 'unknown'

请注意,我假设您unknown在结果中发布了错误的ID