Question

Is there a quick way to make sure the records you return from a MySQL JOIN query are unique?

The code below could potentially bring back the same category twice. Its the category ID which should be distinct!

SELECT 
   exp_categories.cat_name, exp_categories.cat_id, exp_categories.cat_url_title
  ,exp_category_posts.entry_id, exp_channel_titles.status 
FROM (exp_categories 
LEFT JOIN exp_category_posts 
       ON exp_categories.cat_id = exp_category_posts.cat_id) 
LEFT JOIN exp_channel_titles 
       ON exp_category_posts.entry_id = exp_channel_titles.entry_id 
WHERE exp_categories.group_id = 2 
  AND exp_category_posts.entry_id IS NOT NULL 
  AND exp_channel_titles.status = 'open' 
ORDER BY RAND() 
LIMIT 2

Answer 1

    SELECT 
   exp_categories.cat_name, exp_categories.cat_id, exp_categories.cat_url_title
  ,exp_category_posts.entry_id, exp_channel_titles.status 
FROM (exp_categories 
LEFT JOIN exp_category_posts 
       ON exp_categories.cat_id = exp_category_posts.cat_id) 
LEFT JOIN exp_channel_titles 
       ON exp_category_posts.entry_id = exp_channel_titles.entry_id 
WHERE exp_categories.group_id = 2 
  AND exp_category_posts.entry_id IS NOT NULL 
  AND exp_channel_titles.status = 'open' 
  GROUP BY exp_categories.cat_id
ORDER BY RAND() 
LIMIT 2

edit: Adding the column you want to be distinct in the GROUP BY clause will ensure there’s only 1 returned. Also, the ORDER BY RAND() is heavily discouraged, see: http://www.titov.net/2005/09/21/do-not-use-order-by-rand-or-how-to-get-random-rows-from-table/