正确的查询在用作子查询时会产生语法错误

Question

首先，我有这个查询，它工作得很好：

DELETE FROM notifications
WHERE data @> '{"postID": 321}'
RETURNING user_id, read

但是，我将它用作子查询：

SELECT d.user_id, count(d.user_id)
FROM (
    DELETE FROM notifications
    WHERE data @> '{"postID": 321}'
    RETURNING user_id, read
) as d
WHERE d.read = false
GROUP BY d.user_id

并得到这个错误：

ERROR:  syntax error at or near "FROM"
LINE 16:  DELETE FROM notifications
                 ^
SQL state: 42601
Character: 245

1. 我该如何解决这个问题并达到预期的效果？
2. 一般来说，正确的查询如何变成不正确的子查询？

Answer 1

使用 CTE：

WITH d as (
      DELETE FROM notifications
      WHERE data @> '{"postID": 321}'
      RETURNING user_id, read
     ) 
SELECT d.user_id, count(d.user_id)
FROM d
WHERE d.read = false
GROUP BY d.user_id