Question

我有一张用户权限表。这些权利可以是写或读。我有一个合并profile_user表和right_user表的SQL视图。该视图给我以下结果：

+-------+-----------+---------------+
| email | right     | write_or_read |
+-------+-----------+---------------+
| admin | dashboard | write         |
+-------+-----------+---------------+
| admin | dashboard | read          |
+-------+-----------+---------------+
| admin | log       | read          |
+-------+-----------+---------------+

我如何不重复dashbord写入以仅获得最重要的写入权限（写入权限）。我想编写一个SQL查询，它给我以下结果：

+-------+-----------+---------------+
| admin | dashboard | write         |
+-------+-----------+---------------+
| admin | log       | read          |
+-------+-----------+---------------+

我读了this question，但答案仅涵盖id数字字段以获取正确的记录。

Answer 1

在这种情况下，一个简单的max()可以工作：

select email, right, max(write_or_read)
from user_rights
group by email, right;

Answer 2

您可以使用CASE表达式优先列出条件。这也适用于两个以上的值：

SELECT email, right, CASE
    WHEN SUM(write_or_read = 'write') > 0 THEN 'write'
    WHEN SUM(write_or_read = 'read')  > 0 THEN 'read'
    -- more conditions
END AS permission
FROM t
GROUP BY email, right

MySQL选择重复值中的一个字段

2 个答案: