当数据存在时，内部联接返回空集

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)

为什么它是一套空的？从技术上讲，我不应该后退一排吗？

编辑：

如果不使用单引号(如建议(，我会得到以下错误：

ERROR:  column comments.postpostid does not exist
LINE 1: SELECT * FROM comments INNER JOIN posts ON comments.postPost...
^
HINT:  Perhaps you meant to reference the column "comments.postPostId".

Answer 1

通过在'中包装列名，您可以比较这些文字，这总是会产生false。只需放下':

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