选择加入

Question

我真的不知道该怎么解释我需要什么，而不为例做，所以我希望我能解释自己不够好！

可以说我有以下各表在我的MySQL数据库：

buyers 
sellers 
adverts 
addresses 
locations 
object_addresses 

的表格buyers，sellers和adverts都是 “对象”。它们由object_addresses具有object_type，object_id和address_id与addresses有关。

的addresses表具有location_id将其与位置相关联。

我最终想要的是选择在一定距离内的所有类型的对象（通过使用我在locations表中的经度和纬度）。

我没有与距离计算本身就是一个问题。但是，我无法选择所有“对象”以及它们各自的地址/位置（因为它们都使用object_address）。

我能够做到以下几点：

SELECT * FROM buyers as b 
INNER JOIN object_addresses as oa on oa.ObjectId = b.Id 
INNER JOIN addresses as a on oa.AddressId = a.Id 
INNER JOIN locations as l on a.LocationId = l.Id 
WHERE oa.ObjectType = 'buyer'; 

我有结合sellers和adverts到上面的语句很难。

这可能是一个简单的答案，但我就是不能看到它今晚。任何人都可以将我指向正确的方向吗？

Answer 1

SELECT * FROM buyers as b 
INNER JOIN object_addresses as oa on oa.ObjectId = b.Id 
INNER JOIN addresses as a on oa.AddressId = a.Id 
INNER JOIN locations as l on a.LocationId = l.Id 
WHERE oa.ObjectType = 'buyer' 
union 
SELECT * FROM sellers as s 
INNER JOIN object_addresses as oa on oa.ObjectId = s.Id 
INNER JOIN addresses as a on oa.AddressId = a.Id 
INNER JOIN locations as l on a.LocationId = l.Id 
WHERE oa.ObjectType = 'seller' 

etc？

，如果你不喜欢这样 - 基本上，你需要包括地址位多次 - 使每一个可以链接到每个对象类型...

Answer 2

使用连接特定条件试试这个oa.ObjectType = 'seller',oa.ObjectType = 'advert',oa.ObjectType = 'buyer'所以只有相关的结果集将加入

SELECT * FROM buyers as b 

INNER JOIN object_addresses as oa on (oa.ObjectId = b.Id AND oa.ObjectType = 'buyer') 
INNER JOIN advert as ad on (oa.ObjectId = ad.Id AND oa.ObjectType = 'advert') 
INNER JOIN seller as s on (oa.ObjectId = s.Id AND oa.ObjectType = 'seller') 
INNER JOIN addresses as a on oa.AddressId = a.Id 
INNER JOIN locations as l on a.LocationId = l.Id 

其他的解决办法是加入所有的表，然后检查对象类型

SELECT * FROM buyers as b 

INNER JOIN object_addresses as oa on (oa.ObjectId = b.Id) 
INNER JOIN advert as ad on (oa.ObjectId = ad.Id) 
INNER JOIN seller as s on (oa.ObjectId = s.Id) 
INNER JOIN addresses as a on oa.AddressId = a.Id 
INNER JOIN locations as l on a.LocationId = l.Id 
WHERE oa.ObjectType IN('buyer' , 'advert' , 'seller')