Question

Whats wrong with this SQL? It should return results but returns nothing

SELECT `pid` 
  FROM `products` 
  LEFT JOIN `prods_to_features` 
    ON (`ptf_pid` = `pid`) 
 WHERE (   `ptf_id` = '66' 
        OR `ptf_id` = '67'
       ) 
   AND (`ptf_id` = '76')

Is it not possible to have the 2nd where clause for the table that has been used in the left join?

Answer 1

As others have said, the WHERE clause makes no sense.

I’m going to guess that what you’re trying to say is you want products that have a feature-76 AND have a feature 66-or-67. You will need two joins for that:

SELECT DISTINCT products.pid
FROM products
JOIN prods_to_features AS ptf1 ON ptf1.ptf_pid=products.pid
JOIN prods_to_features AS ptf2 ON ptf2.ptf_pid=products.pid
WHERE ptf1.ptf_id='76'
AND ptf2.ptf_id IN ('66', '67')

The DISTINCT is to ensure only one copy of a product is returned in the case where a product has both features 66 and 67.