子查询返回NULL “NOT IN”

Question

这里是我的查询

select distinct(Challan_No) 
from Challan_tb 
where Challan_No not in 
    (
    select Challan_No from Invoice_tb where Customer_ID =2 and InvYear=2013 
) and InvYear=2013 and Customer_ID =2 

子查询返回NULL所以外部查询不工作

请帮

Answer 1

有一个简单的，明显的修复，如果你不想改变查询的结构太多：

select distinct(Challan_No) 
from Challan_tb 
where Challan_No not in 
    (
    select Challan_No from Invoice_tb where Customer_ID =2 and InvYear=2013 
    and Challan_No is not null --This line is new 
) and InvYear=2013 and Customer_ID =2 

Answer 2

你可以尝试一个LEFT JOIN代替。我认为Access会更好地消化这个。

select distinct(Challan_tb.Challan_No) 
from Challan_tb 
left join Invoice_tb on Invoice_tb.Challan_No = Challan_tb.Challan_No 
where Challan_tb.InvYear=2013 and Challan_tb.Customer_ID=2 
and Invoice_tb.InvYear is null --or any other Invoice_tb field