sql - Postgres : Group by on a column but query needs to return all columns in the table

Question

我有一个具有以下结构的表:

id, user_id, connected_id, completed
1, 2345, 232, t
2, 2345, 121, f
3, 4324, 123, t
4, 4324, 121, t
5, 1211, 134, f
6, 1211, 111, t

有没有办法通过 user_id 获取表组的所有列。因为我 group by 的列必须在子句中。有解决办法吗。

我试图构建以下结果集:

user_id, total_completed

我想我会做一个两阶段的过程，因为我实际上是通过 mybatis 访问数据。

Answer 1

看来你需要的是

  SELECT user_id,
         COUNT(CASE WHEN completed THEN 1 END) total_completed
    FROM tablename
GROUP BY user_id