Question

Can somebody explain me this. My SQL:

SELECT 
    `offers`.`id`, 
    `offers`.`max_available`, 
    (SELECT COUNT( coupons.id ) FROM coupons WHERE coupons.status = 'Y' AND coupons.offer_id = offers.id) AS coupons_sold
FROM 
    `offers`
WHERE 
    `offers`.`status` IN ('P', 'S') AND 
    `offers`.`published_at` < 1341612000 AND 
    `offers`.`end_at` >1341567914 AND 
    `coupons_sold` < `offers`.`max_available` 
ORDER BY `offers`.`created_at` DESC
LIMIT 4 OFFSET 0 

This will return me these 4 rows:

id      max_available   coupons_sold
195     19              20
194     9999            0
193     9999            0
159     9999            93

How is possible that row with ID 195 is included, if I have this condition in where coupons_sold < offers.max_available? I am clueless!

Answer 1

This query would produce an error, as you can’t use in WHERE clause, an alias from the SELECT list. Unless table offers has a coupons_sold column, too!

Try this query, instead:

SELECT id, max_available, coupons_sold
FROM
  ( SELECT 
        `offers`.`id`, 
        `offers`.`max_available`, 
        ( SELECT COUNT( coupons.id ) 
          FROM coupons 
          WHERE coupons.status = 'Y' 
            AND coupons.offer_id = offers.id
         ) AS coupons_sold
         offers.created_at
    FROM 
        `offers`
    WHERE 
        `offers`.`status` IN ('P', 'S') AND 
        `offers`.`published_at` < 1341612000 AND 
        `offers`.`end_at` >1341567914
  ) AS tmp
WHERE coupons_sold < max_available 
ORDER BY created_at DESC
  LIMIT 4 OFFSET 0 ;