SQL調試 - 忽略條件

Question

有人可以解釋我這個。我的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 

這將返回我這4行：

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

怎麼可能與ID 195行被包括在內，如果我有在coupons_sold < offers.max_available這種狀況呢？我無能爲力！

Answer 1

此查詢會產生一個錯誤，因爲您不能在WHERE子句中使用，該子句是SELECT列表中的別名。除非表offers也有coupons_sold列！

嘗試此查詢，而不是：

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 ;