Subquery on a join

Question

I'm trying to do a query to filter on rows from one table and then join the results on another table and then filter out additional rows.

Here is the query I've written:

SELECT * 
  FROM (SELECT media.id AS id2, media.flagged AS flagged2, media.item_status AS status2 
          FROM media 
         WHERE flagged2 != 'nsfw' 
           AND status2 != 'deleted' 
     ORDER BY id2 DESC LIMIT 0,5) 
  JOIN media on info.mid = media.id 
 WHERE info.topic = 'food_drink' 
    OR info.topic='cooking' 
GROUP BY info.mid

I think I'm pretty close to getting the query working but I keep getting the message, "Every derived table must have its own alias." I've Googled this and from what I've read I need to alias parts of the subquery which I've tried but I still can't get it working.

Answer 1

Use:

SELECT * 
  FROM (SELECT media.id AS id2, media.flagged AS flagged2, media.item_status AS status2 
          FROM media 
         WHERE flagged2 != 'nsfw' 
           AND status2 != 'deleted' 
      ORDER BY id2 DESC LIMIT 0, 5) x
  JOIN media on info.mid = media.id 
 WHERE info.topic = 'food_drink' 
    OR info.topic='cooking' 
GROUP BY info.mid

See the x , just outside the bracket but before the join? That's what the error is about. The stuff inside the brackets after FROM and before JOIN is a derived table (AKA inline view), and MySQL requires that you specify a table alias for it. Then, when you reference any columns from inside it, you'd use x.id2 /etc.