的日期SQL返回null

Question

我有以下查询：

select EL.Datetimestart, E.Fullname, VisaExpiryDate, E.EmployeeStatusCode 
from EmployeeLog as EL 
inner join Employee as E on E.Employeekey = EL.EmployeeKey 
where DateTimeStart >= Getdate() -1 and VisaExpiryDate <=GetDate() and E.EmployeeStatusCode <> 'x' 
order by VisaExpiryDate 

目前，这将返回谁拥有签证过期，并在这一天的工作的员工，

VisaExpiryDate - 2017-08-08 00:00:00.000 
DateTimeStart - 2017-08-10 08:00:03.090 
FullName - Rypsuke 
EmployeeStatusCode - C 

签证信息检查并插入到系统中，这可能需要几天时间，因此新员工将空白字段留空。

我该如何回复这些空值以查看谁还没有签证检查和签证过期的人？

感谢您的帮助。如果我理解正确 尼克

Answer 1

使用IS NULL

select EL.Datetimestart, E.Fullname, VisaExpiryDate, E.EmployeeStatusCode 
from EmployeeLog as EL 
inner join Employee as E on E.Employeekey = EL.EmployeeKey 
where DateTimeStart >= Getdate() -1 and (VisaExpiryDate <=GetDate() OR VisaExpiryDate IS NULL)and E.EmployeeStatusCode <> 'x' 
order by VisaExpiryDate 

Answer 2

，你可以再补充一个条件到where条款：

select EL.Datetimestart, E.Fullname, VisaExpiryDate, E.EmployeeStatusCode 
from EmployeeLog EL inner join 
    Employee E 
    on E.Employeekey = EL.EmployeeKey 
where DateTimeStart >= Getdate() - 1 and 
     (VisaExpiryDate <= GetDate() or VisaExpiryDate is null) and 
     E.EmployeeStatusCode <> 'x' 
order by VisaExpiryDate;