Question

以下查询仅在我在表wm_purchased_products.purchased_article_id中有引用时才起作用，但是当它为空时，mysql_num_rows返回0

查询是：

  SELECT (SUM(wm_products_quantities.new_quantity) - SUM(wm_purchased_products.purchased_article_total) ) AS stock_restante, 
         wm_products_wall.nombre, 
         wm_products_wall.detalles, 
         wm_products_wall.price, 
         wm_products_wall.image_full, 
         wm_products_wall.fecha, 
         wm_products_wall.article_hashid
    FROM wm_products_wall,
         wm_products_quantities, 
         wm_purchased_products 
   WHERE wm_products_wall.categoria = '$new_rquery_xp' 
     AND wm_products_wall.article_hashid = wm_products_quantities.hashid_ref 
     AND wm_products_wall.article_hashid = wm_purchased_products.purchased_article_id 
GROUP BY wm_products_wall.article_hashid 
ORDER BY stock_restante ASC

如果表wm_purchased_products.purchased_article_id

中没有记录，如何构建此查询

Answer 1

您的代码FROM wm_products_wall, wm_products_quantities, wm_purchased_products表示所有三个表都是INNER JOIN。（也就是说，第一个表中的每一行都连接到第二个表中的每一行，依此类推。）

你可以让wm_products_wall LEFT JOIN与wm_purchased_products，wm_purchased_products也是如此。

SELECT 
(SUM(wm_products_quantities.new_quantity) - SUM(wm_purchased_products.purchased_article_total) ) AS stock_restante, 
wm_products_wall.nombre, wm_products_wall.detalles, wm_products_wall.price, 
wm_products_wall.image_full, wm_products_wall.fecha, 
wm_products_wall.article_hashid
FROM wm_products_wall
LEFT OUTER JOIN wm_products_quantities
  ON wm_products_wall.article_hashid = wm_products_quantities.hashid_ref 
LEFT OUTER JOIN wm_purchased_products
  ON wm_products_wall.article_hashid = wm_purchased_products.purchased_article_id
WHERE wm_products_wall.categoria = '$new_rquery_xp' 
GROUP BY wm_products_wall.article_hashid 
ORDER BY stock_restante ASC

在这个查询MYSQL中失败了什么

1 个答案: