drmrkrch

SELECT p.product_id, SUM(s.quantity) AS 'sale', SUM(p.quantity) AS 'purchase' FROM purchase p LEFT JOIN sale s ON (s.product_id=p.product_id) GROUP BY p.product_id; This should give you what you need.

You are defining your SQL statement in line 13 however you're not executing it. It would be mysql_query ($sql); Consult your version of php for the exact syntax as some intrinsic functions are depreciated with certain versions.

You will need to do an outer join select all from one table while getting the matches from another. Why are you joining on company name instead of an I'd value? Mark