joining a count on a query
Question
I have 2 tables: comments & blog
blog has the following fields: id(Unique key),title, author, body, date, img, imgdes, tags
comments : key(Unique key), postid(related to the id of blog),name, email, date, message
Im trying to display all of my blog post and the number of comments on every post.
So im trying to "count(postid) where postid=id"
I got something to work but its based around having 1 comment which wont work but this is it:
SELECT a.postid,c.author,c.title, c.id,c.body,c.date,c.pic, c.tags, c.imgdesc,
COUNT(*) AS num_comments FROM comments a LEFT JOIN blog c ON c.id = a.postid
GROUP BY c.id order by id DESC"
Again this only work when everything has a comment and i get why but i cant figure out how to implement what I want.
To put it all out there i have:
$sql="***( help 1 of 2) what to set the query to****"
$query = mysql_query($sql) or die(mysql_error());
<?php do{ ?>
<html stuff here>
<?php echo $blog['title']?><br>
<?php echo $blog['*******(help 2 of 2) # of comments display here******']
<?php } while($blog = mysql_fetch_assoc($sql));?>
im sure this is a easy join but i have no clue thanks!
4 answers
solution1
1 ACCPTED 2012-07-23 04:57:06
使用此查询它可能适合您
SELECT a.postid,c.author,c.title, c.id,c.body,c.date,c.pic, c.tags, c.imgdesc, COUNT(a.key) AS num_comments FROM blog c left outer join comments a ON a.postid = c.id GROUP BY c.id order by id DESC
solution2
1 2012-07-23 04:57:23
如果你想要所有博客文章，那么它应该在左连接的左侧。
solution3
0 2012-07-23 04:56:42
I think the issue lies where you write: FROM comments a LEFT JOIN blog c ON c.id = a.postid GROUP BY c.id order by id DESC"
The comments a and blog c don't seem to be correct references.
Should it be FROM comments.a LEFT JOIN blog.c ON ...?
solution4
0 2012-07-23 05:10:51
Are you trying to count the number of comments in each blog? if yes then, SELECT c.postid,count(key) as num_of_comments FROM blog b, comments c WHERE b.id = c.postid GROUP BY c.postid
Another easy way out: As you have the postid as a foreign key, you can just get the results from comments table SELECT postid,count(key) as num_of_comments FROM comments GROUP BY postid
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