SQL：如何将查询的值用作另一个查询的字段？

Question

user_object：

id | group | object_id 
-----+--------+------------ 
    1 | admin | 30 
    2 | user | 40 
    3 | user | 50 

object_permissions：

id | name | user | admin 
------+------+--------+-------- 
    30 | foo | false | true 
    40 | bar | false | false 
    50 | baz | true | true 

我希望上面的例子帮助。我想要下面的东西。我想，如果甚至有可能会有子查询和可能的评估。

SELECT u.id 
    , o.name 
    , o.<u.group>  as permissions 
FROM user_object  u 
JOIN object_permissions o 
     ON (u.object_id = o.id); 
---------------------------- 
    id | name | permissions 
-----+-------+-------------- 
    1 | foo | true 
    2 | bar | false 
    3 | baz | true 

Answer 1

假设管理员/用户是出现在user_object的组列中的唯一值，尝试：

SELECT u.id 
    , o.name 
    , CASE WHEN u.group = 'admin' 
      THEN o.admin 
      ELSE o.user 
     END AS permissions 
FROM user_object  u 
JOIN object_permissions o 
     ON (u.object_id = o.id);