小编Krz*_*iak的帖子

如何告诉 PostgreSQL 返回第一个遇到的值而不是聚合列？

                          Table "public.cache"
  Column   |  Type   | Modifiers | Storage | Stats target | Description 
-----------+---------+-----------+---------+--------------+-------------
 user_id   | integer |           | plain   |              | 
 object_id | integer |           | plain   |              | 
 data      | integer |           | plain   |              | 
 data2     | boolean |           | plain   |              | 
Indexes:
    "cache_object_id_user_id_key" UNIQUE CONSTRAINT, btree (object_id, user_id)
    "cache_user_id_object_id_key" UNIQUE CONSTRAINT, btree (user_id, object_id)
Has OIDs: no

按 object_id 和 data2 进行查询分组将使哈希聚合，这是我想避免的。

SELECT object_id, data2 FROM cache GROUP BY object_id, data2; …