LEFT JOIN with where clause only for second table

Question

I have two tables:

1. posts (id, title, content, etc)
2. post_meta (id, post_id, meta_key, meta_value)

I want to get with only one query, all the entries from posts and the entries from post_meta only with post_meta='x'. Some of the entries from posts doesn't have correspondent in post_meta, but I need them. I can do this with only one query?

Answer 1

Select a.*, b.* 
From post a 
  left join post_meta b on (a.id = b.id and b.meta_key='x')

Answer 2

select * 
from post 
  left join 
  post_meta 
where isNull(post_meta.meta_value) 
      or 
      post_meta.meta_value ="x"

I haven't done much sql for a while, but I know it is possible. I think it was querying isNull on any value of the table that you are left joining.

Answer 3

select *
from posts p
   left outer join post_meta pm on p.id=pm.post_id and pm.meta_key='x'

Answer 4

试试这个..从post.id = post_meta.post_id上的LEFT JOIN post_meta中选择*，其中post_meta.x ='x'

Answer 5

这是我的解决方案。

SELECT * FROM post,post_meta WHERE post.id=post_meta.post_id , post_meta.id="x";

Answer 6

SELECT posts.*, post_meta.* 
FROM posts 
LEFT JOIN post_meta 
ON posts.id = post_meta.post_id WHERE post_meta.meta_value is null OR
post_meta.meta_value = 'x'

Since you want all the posts from posts table whose corresponding meta_value in post_meta table is either 'x' or meta_value doesn't exists, this should work.