Question

我有以下查询返回产品和最低卖价与销售价格的数量。一切都运作良好，直到我想得到product_price表中没有任何价格的产品。如何退回产品数据和NULLS以获取售价和数量？

SELECT p.*, MIN(pp.sellPrice) as sellPrice, pp.quantity FROM `product` as p
LEFT JOIN `product_price_group` as ppg ON ppg.productId = p.`id`
LEFT JOIN `product_price` as pp ON pp.priceGroupId = ppg.`id`
WHERE p.`id` = 1 AND p.`active` = 1

具有可用价格的产品的输出：

+----+--------------+--------+--------------+--------------+-----------+----------+
| id | name         | active | sortSequence | creationDate | sellPrice | quantity |
+----+--------------+--------+--------------+--------------+-----------+----------+
|  1 | product_id_1 |      1 |            1 |   1287481220 |     22.00 |       10 |
+----+--------------+--------+--------------+--------------+-----------+----------+

无法定价的产品的输出

+----+------+--------+--------------+--------------+-----------+----------+
| id | name | active | sortSequence | creationDate | sellPrice | quantity |
+----+------+--------+--------------+--------------+-----------+----------+
| NULL | NULL | NULL |         NULL |         NULL |      NULL |     NULL |
+----+------+--------+--------------+--------------+-----------+----------+

期望的输出：

+----+--------------+--------+--------------+--------------+-----------+----------+
| id | name         | active | sortSequence | creationDate | sellPrice | quantity |
+----+--------------+--------+--------------+--------------+-----------+----------+
|  2 | product_id_2 |      1 |            1 |   1287481220 |     NULL  |     NULL |
+----+--------------+--------+--------------+--------------+-----------+----------+

更新看来我正在选择不存在的产品！非常愚蠢。

Answer 1

如何在product_price表中使用LEFT OUTER JOIN？

SELECT p.*, MIN(pp.sellPrice) as sellPrice, pp.quantity FROM `product` as p
LEFT JOIN `product_price_group` as ppg ON ppg.productId = p.`id`
LEFT OUTER JOIN `product_price` as pp ON pp.priceGroupId = ppg.`id`
WHERE p.`id` = 1 AND p.`active` = 1

这是你想要的吗？

更新：修订 - 与其他人一样，LEFT JOIN = LEFT (OUTER) JOIN所以在这种情况下它不会帮助你......

Answer 2

我可能不正确，但我对LEFT JOIN的理解一直是在SQL语句中编写的等式测试中的表引用...另外，我是如何编写查询的......从表开始我期待FIRST（左），加入OTHER（右）表第二...保持连接条件也是该关系的各个...

select from x left join y where x.fld = y.fld
   instead of 
select from x left join y where y.fld = x.fld

所以我会按如下方式调整您的查询

SELECT
      p.*, 
      MIN(pp.sellPrice) as sellPrice, 
      pp.quantity 
   FROM 
      product as p
         LEFT JOIN product_price_group as ppg 
            ON p.id = ppg.productId
            LEFT JOIN product_price as pp 
               ON ppg.id = pp.priceGroupId
   WHERE 
          p.id = 1 
      AND p.active = 1

此外，您可以使用IFNULL（字段，0）包装min（）和数量，以防止显示NULLS，但实际上是零值。

加入SQL查询问题

2 个答案: