Mysql Tag Query - Repeated values

I'm working on a tag-based search. The user can search one tag or multiple tags. I've got 3 tables: Content, Content_Tags and Tags. Content_Tags does the link between content and tags. The query has to return all the information of the content retrieved, this includes a concatenated string of all tags from that content.

Using an example from other question I've managed to reach this q开发者_JAVA技巧uery:

SELECT content.Name,GROUP_CONCAT(t2.Tag SEPARATOR ' ') FROM content 
JOIN content_tags ct1 ON content.ContentID = ct1.ContentID 
JOIN tags t1 on ct1.TagID = t1.TagID AND t1.Tag IN('grass','texture') 
JOIN content_tags ct2 ON ct2.ContentID = content.ContentID JOIN tags t2 ON ct2.TagID = t2.TagID GROUP BY content.ContentID;

The query works fine when searching for 1 tag, but using IN('grass','texture') the GROUP_CONCAT will return 'grass grass texture texture' (repeating the tags). I don't know MySQL this deep, how could I fix this problem?

SELECT  content.name,
        (
        SELECT  GROUP_CONCAT(cta.tag)
        FROM    content_tags cta
        WHERE   cta.contentID = ct.contentID
        )
FROM    content_tags ct
JOIN    content c
ON      c.contentId = ct.contentId
WHERE   ct.tag IN ('grass', 'texture')
GROUP BY
        ct.contentId
HAVING  COUNT(*) = 2