Left join, sum and count group by

Question

I have 3 tables: goods, store and pics. In the first table goods titles are stored. In the second - balance of goods in different stocks, in the third - links to goods pictures.

Answer 1

Your issue is that when you have two (or more) store rows and two (or more) pics rows for a single goods row, you end up with the product of all the combinations of rows.

To fix this, do your aggregation before joining:

SELECT 
  good.id, 
  good.title, 
  IFNULL(s.storerest, 0) AS storerest, 
  IFNULL(p.picscount, 0) AS picscount
FROM goods 
LEFT JOIN (
  SELECT goodid, sum(rest) AS storerest
  FROM store
  GROUP BY goodid
) s ON (goods.id = s.goodid) 
LEFT JOIN (
  SELECT goodid, count(id) AS picscount
  FROM pics
  GROUP BY goodid
) p ON (goods.id = p.goodid)