If groupby does not meet the condition, he does not return data, for example, posts Post table.
Create table posts (
Posts_id,
Forumid, (Forum ID)
Posts_title,
Posts_postTime,
)
Comments comment table
Create table comments (
Comments_id,
Postsid,
Comments_content,
Comments_postTime,
)
The result is: read all posts with Forum ID 1 and count the total number of comments for each post.
I use count (comments_id) AS commentsNum to count comments. However, if no comments are posted in the comments table, group by ignores the comments.
Posts_id forumid commentsNum
1 1 4
2 1 5
3 1 4
4 1 0
I want to return 0 or Null when The Post has no comment in the comment table. how can this problem be solved?
Reply to discussion (solution)
Select. posts_id,. forumid, count (B. comments_id) as commentsNum from posts a left join comments B on. posts_id = B. postsidgroup by B. postsid having. forumid = 1
Solved the problem. thanks to the moderator, Having was not used =
