SQL left join and group_concat returns duplicate data

Question

I am trying to return data from 3 different tables with 2 left joins. All tables return multiple rows. Here is my statement:

SELECT s.*, GROUP_CONCAT(sp.photo) AS photos, GROUP_CONCAT(st.name) AS tags
FROM sites s
LEFT JOIN sites_photos sp
ON sp.sites_id = s.id
LEFT JOIN sites_tags st
ON st.sites_id = s.id
WHERE s.id = 30

The data this statement returns looks like:

Array
(
[id] => 30
[url] => www.test.be
[name] => test
[date] => 2014-08-16
[photos] => 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132191_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg, 201408141132194_gummies.jpg
[tags] => test, hello, ale, print, social, more, hcp, test, hello, ale, print, social, more, hcp
)

Like you can see "tags" are returned twice and the "photos" more than 5 times. When I remove one LEFT JOIN the query returns the right data. How can prevent the statement from returning duplicate data?

Thanks in advance.

Answer 1

Use

GROUP_CONCAT(DISTINCT sp.photo) AS photos, GROUP_CONCAT(DISTINCT st.name)