Question

大家好，我有桌子，上面有产品和价格。我所要做的就是显示每种产品的最低价格，如果它没有出现在价格表中，则显示价格为null的产品这是我写的一个查询

SELECT 
t15_catalogue_line.T15_GROUP, sc_products.product_code,sc_products.unic, 
sc_products.name_ru, UPPER(TRIM(sc_products.brief_description_ru)) AS 
brief_description_ru, sc_products.suupplier, price.Price, 
sc_group_discounts.`action`, sc_group_discounts.procent,
sc_products.productID, price.in_stock, price.supplier, t10_item.T10_ITEM, 
t10_item.unic, t10_item.T10_DESC, t10_item.T10_IMG, t10_item.T10_ITEM_GROUP, 
t10_item.T10_FIELD1, t10_item.T10_FIELD2, t10_item.T10_FIELD3, 
t10_item.T10_FIELD4, t10_item.T10_FIELD5, t10_item.T10_FIELD6, 
t10_item.T10_FIELD7, t10_item.T10_FIELD8, t10_item.T10_FIELD9, 
t10_item.T10_FIELD10, t10_item.T10_FIELD11, t14_item_fields.T14_ITEM_GROUP, 
t14_item_fields.T14_FIELD, t14_item_fields.T14_NAME, 
t14_item_fields.T14_UNIT, t14_item_fields.T14_SEARCH 
FROM sc_products 
LEFT OUTER JOIN t15_catalogue_line ON (sc_products.unic = t15_catalogue_line.unic) 
LEFT OUTER JOIN price ON (sc_products.product_code = price.item) AND (sc_products.suupplier = price.postavchik)
LEFT OUTER JOIN sc_group_discounts ON (sc_products.item_group = sc_group_discounts.item_group)
LEFT OUTER JOIN t10_item ON (sc_products.unic = t10_item.unic and sc_products.CatText=t10_item.CatText)
LEFT OUTER JOIN t14_item_fields ON (t10_item.T10_ITEM_GROUP = t14_item_fields.T14_ITEM_GROUP) 
WHERE sc_products.CatText = 'bearing' 
AND t15_catalogue_line.T15_CARTYPE = '42769' 
AND t15_catalogue_line.T15_GROUP = '546678' and sc_products.unic is not null and sc_products. unic!='' and 
CASE WHEN price.Price is null then price.Price is null else price.Price=(SELECT 
MIN(price.Price) from price where price.unic=sc_products.unic 
AND price.CatText='bearing') end 
GROUP BY sc_products.unic 
ORDER by isnull (price.Price),price.Price ASC

现在它只显示那些价格为null的其他声明并不起作用。

Answer 1

在case中，您必须使用THEN NULL，而不是THEN price.Price IS NULL：

 AND CASE
        WHEN price.Price IS NULL THEN NULL
        ELSE
           (
                SELECT
                    MIN(price.Price)
                FROM
                    price
                WHERE
                    price.unic = sc_products.unic
                AND price.CatText = 'bearing'
            )
    END

您应使用AND条件，而不是结束案例，如下所示：

AND (    ( price.CatText = 'bearing' AND  price.unic = sc_products.unic) 
      OR ( price.CatText = 'bearing' AND  price.unic is numm)  )

并最终选择min（your_value）应该在select子句中，而不是在where中。

Answer 2

另一个答案很接近......你可能需要通过额外的LEFT-JOIN来做到这一点，你的ELSE子选择是......

LEFT JOIN （选择 price.unic， MIN（price.Price）为minprice 从价钱哪里 price.CatText =＆＃39;承载＆＃39; 通过...分组 price.unic）ByUnic ON sc_products.unic = ByUnic.unic

然后你的案例的INSTEAD /当WHERE子句时，删除它。更改字段选择属性，将价格从... price.price改为：

  COALESCE( price.Price, ByUnic.minPrice ) as Price

这将首先返回price.price字段。如果为null，则返回左连接表的值ByUnic，minPrice结果如果它存在，否则仍为null。如果您想要在Price.Price之前的最低价格，只需交换字段顺序，如

  COALESCE( ByUnic.minPrice, price.Price ) as Price

else语句在mysql中不起作用

2 个答案: