Question

I have three MySQL tables, one with data, one with tags and one with associations between those two, which seems to be common practice when storing tags. The tables look like this:

links:
+----+------------+------------+
| id | url        | added      |
+----+------------+------------+
| 2  | google.com | 2012-12-14 |
| 3  | cnn.com    | 2001-02-13 |
+----+------------+------------+

tags:    
+----+--------+
| id | tag    |
+----+--------+
| 1  | search |
| 2  | news   |
+----+--------+


taglink:
+----+--------+-------+
| id | linkid | tagid |
+----+--------+-------+
| 1  | 2      | 1     |
| 2  | 3      | 1     |
| 3  | 3      | 2     |
+----+--------+-------+

What I want to receive is the following table:

+----+------------+------------+--------+-------------+
| id | url        | added      | tagids | tags        |
+----+------------+------------+--------+-------------+
| 2  | google.com | 2012-12-14 | 1      | search      |
| 3  | cnn.com    | 2001-02-13 | 1,2    | search,news |
+----+------------+------------+--------+-------------+

To do so I had this query:

select 
   links.*,
   group_concat(taglink.id) as tagids,
   group_concat(tags.tag) as tags
from links
   join taglink on taglink.linkid=links.id
   join tags on tags.id=taglink.tagid

but this gives me a single row with every tag used, like so:

+----+------------+------------+--------+-------------+
| id | url        | addad      | tagids | tags        |
+----+------------+------------+--------+-------------+
| 2  | google.com | 2012-12-14 | 1,2    | search,news |
+----+------------+------------+--------+-------------+

Everything seems to be grouped, which is not what I was looking for. Does anybody know the solution?

Answer 1

You need to use GROUP BY with your group_concat functions as follows, or they’ll behave unpredictably. Try this.

    select links.id, links.url, links.added,
           group_concat(tags.id ORDER BY tags.id) as tagids,
           group_concat(tags.tag ORDER BY tags.id) as tags
      from links
      join taglink on taglink.linkid=links.id
      join tags on tags.id=taglink.tagid
  group by links.id, links.url, links.added
  order by links.id

Note that I’ve added some ORDER BY items to make the order of things predictable.

Go fiddle: http://sqlfiddle.com/#!2/2b3b9/5/0