Question

我有一个mysql查询，可以从2个表，'properties'和'offers'进行交互。

'要约'表可以匹配属性表中的记录，方法是通过唯一代码或属性所在的县或地区引用特定记录。

以下是我的查询示例...

SELECT *, ROUND(((3959 * acos(cos(radians(51.1080390)) * cos(radians(latitude)) * cos(radians(longitude) - radians(-4.1610140)) + sin(radians(51.1080390)) * sin( radians(latitude)))) * 2),0)/2 AS `distance`
FROM `properties` AS prop
LEFT JOIN `offers` ON prop.code = offers.the_property
LEFT JOIN `offers` AS offsCnty ON prop.county = offsCnty.the_county
LEFT JOIN `offers` AS offsRgn ON prop.region = offsRgn.the_region
HAVING distance <= 2.5
ORDER BY `sleeps` ASC, `distance` ASC
LIMIT 0, 10

在商品表中，3列the_property / the_county / the region对于将相应商品与商品/商家相关联至关重要。如果要将报价应用于整个县，则字段the_property为空白，否则如果报价针对特定属性，则此字段包含唯一的属性代码。

我认为通过使用多个JOIN将是解决方案，但是当3个主offer字段中的任何一个为空时，连接将为offers表字段返回'NULL'。

如何解决？

非常感谢

Answer 1

您可以加入这两个表，并在join子句或where子句

中指定额外的连接条件

SELECT *, ROUND(((3959 * acos(cos(radians(51.1080390)) * cos(radians(latitude)) * cos(radians(longitude) - radians(-4.1610140)) + sin(radians(51.1080390)) * sin( radians(latitude)))) * 2),0)/2 AS `distance`
FROM `properties` AS prop
LEFT JOIN `offers` ON prop.code = offers.the_property 
       OR prop.county = offers.the_county 
       OR prop.region = offers.the_region
HAVING distance <= 2.5
ORDER BY `sleeps` ASC, `distance` ASC
LIMIT 0, 10

Answer 2

以后提供的表格会覆盖之前的表格，您需要为它们添加别名：

SELECT *，offers.the_property the_property_from_offers，...

Answer 3

您有三个不同的商品表，所有商品都具有相同的字段名称。问题是MySQL不允许多个具有相同名称的列。

最简单的解决方法是更改联接以在or子句中使用on：

SELECT *, ROUND(((3959 * acos(cos(radians(51.1080390)) * cos(radians(latitude)) * cos(radians(longitude) - radians(-4.1610140)) + sin(radians(51.1080390)) * sin( radians(latitude)))) * 2),0)/2 AS `distance`
FROM `properties` prop LEFT JOIN
     `offers`
      ON prop.code = offers.the_property or
         (prop.county = offsCnty.the_county and offers.the_property is null) or
         prop.region = offsRgn.the_region
HAVING distance <= 2.5
ORDER BY `sleeps` ASC, `distance` ASC
LIMIT 0, 10;

如果您确实使用了多个连接，那么您应该在select子句中包含以下表达式：

select coalesce(offers.code, offsCnty.code, offsRgn.code) as code

对于商品表中的每一列。

Answer 4

如果您希望最具体的报价优先，我认为您必须这样写：

SELECT prop.*,
       COALESCE(offers.col1, offsCnty.col1, offsRgn.col1) col1,
       COALESCE(offers.col2, offsCnty.col2, offsRgn.col2) col2,
       ...,
       <huge formula> distance
FROM `properties` AS prop
LEFT JOIN `offers` ON prop.code = offers.the_property
LEFT JOIN `offers` AS offsCnty ON prop.county = offsCnty.the_county
LEFT JOIN `offers` AS offsRgn ON prop.region = offsRgn.the_region
HAVING distance <= 2.5
ORDER BY `sleeps` ASC, `distance` ASC
LIMIT 0, 10

MySQL在多列上查询多个JOIN两个表

4 个答案: