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',