内部连接在数据存在时返回空集

Question

这是我的查询：

SELECT * 
FROM comments 
  INNER JOIN posts ON 'comments.postPostId' = 'posts.post_id';

所有评论：

blog=# select * from comments;
              comment_id              |                 uid                  |         content         |              postPostId              
--------------------------------------+--------------------------------------+-------------------------+--------------------------------------
 49104d66-aebf-48f5-b816-46d9def8edc2 | 5ef3d422-8b98-4509-a752-5ac8d1aee40d | oh man this game is lit | 1c756322-0042-4d8e-bab8-e04a9ceb981e
(1 row)

所有帖子：

blog=# select * from posts;
               post_id                |                 uid                  | title |   sub_title    | content |              userUserId              
--------------------------------------+--------------------------------------+-------+----------------+---------+--------------------------------------
 1c756322-0042-4d8e-bab8-e04a9ceb981e | 2e83d249-7c7c-43c0-8e3d-854ddac7c1b8 | bf1   | love this game | bla bla | 6cc903a7-11bf-43a4-a75a-3e1456404525
(1 row)

结果：

blog=# SELECT * FROM comments INNER JOIN posts ON 'comments.postPostId' = 'posts.post_id';
 comment_id | uid | content | postPostId | post_id | uid | title | sub_title | content | userUserId 
------------+-----+---------+------------+---------+-----+-------+-----------+---------+------------
(0 rows)

为什么它是一个空集？从技术上来说我不应该退回一排吗？

Answer 1

通过在'中包装列名，您正在比较这些文字，它们总是产生false。稍微放下'：

SELECT * FROM comments INNER JOIN posts ON comments.postPostId = posts.post_id;