Question

.

I have 4 tables as shown above. Now I’m trying to get all the data including article subjects, tags for each article, and number of comments for each article, in ONE query.

The sql query I’m using now is

SELECT
    articles.subject, GROUP_CONCAT(tags.name) AS tags, COUNT(comments.aid) AS comments
FROM articles
    LEFT JOIN comments ON comments.aid = articles.aid
    LEFT JOIN relations ON relations.aid = articles.aid
    LEFT JOIN tags ON tags.tid = relations.tid
GROUP BY
    articles.aid

The result: data in [ ] is what I actually get

array
(
    1 => array
    (
        subject => foo
        tags =>
        comments => 1
    )
    2 => array
    (
        subject => bar
        tags => html,mysql [html,mysql,html,mysql]
        comments => 2 [4]
    )
    3 => array
    (
        subject => baz
        tags => php
        comments => 0
    )
)

For the real situation here in my application, number of tags and number of comments will multiply with each other. For example: if there are 4 comments, and 3 tags in one article, my query will result in

tags: html,css,php, html,css,php, html,css,php, html,css,php (instead of html,css,php)

comments: 12 (instead of 4)

I know there must be something wrong with my query statement, I just don’t know how to fix it.
Someone please help. Thanks.

Answer 1

I think you need a nested query to count the comments

SELECT
    articles.subject, GROUP_CONCAT(tags.tag) AS tags, comments
FROM articles
    LEFT JOIN (
          select aid,count(cid) as comments from comments group by aid
    ) AS commentscount ON commentscount.aid = articles.aid
    LEFT JOIN relations ON relations.aid = articles.aid
    LEFT JOIN tags ON tags.tid = relations.tid
GROUP BY
    articles.aid