sql server, left join on，on附近有语法错误

Question

select cast(Service_Order_No as nvarchar)+CAST(Item_No as nvarchar) as 'Key1', Service_Order_No, Item_No from dbo.GH_Billing_ID_TH_MY_IN as A left join (select cast([Service Order ID] as nvarchar)+CAST([Service Order Line] as nvarchar) as 'Key2', [Service Order ID],[Service Order Line] from dbo.SO_Raw_All as B) on A.Key1= B.Key2;提示：消息 156，级别 15，状态 1，第 8 行关键字 'on

Answer 1

select (cast(Service_Order_No as nvarchar)+CAST(Item_No as nvarchar) )as 'Key1',

Service_Order_No

 

这个地方错了

对应的，这个地方也错了

select (cast([Service Order ID] as nvarchar)+CAST([Service Order Line] as nvarchar)) as 'Key2',