mysql - 在同一查询中使用查询值

Question

如果我有一个包含两个选择的查询，我可以在第二个选择中使用第一个选择中的值吗？

即:

(SELECT post_id AS post_1 FROM posts WHERE user_id = 100) UNION (SELECT post_id AS post_2 FROM posts WHERE user_id = post_1)

上面的方法不起作用，那么我该怎么做呢？

Answer 1

您似乎正在寻找加入？

SELECT p1.post_id as post_id1
     , p2.post_id as post_id2
  FROM posts p1
  JOIN posts p2
    ON p2.user_id = p1.post_id
 WHERE p1.user_id = 100;