How to reference multiple columns in a case expression

Question

I have a query where I am trying to use a case statement that references two columns.

Data:

User table:

ID_User       sUserName
1             Test
2             Test2
3             Test3

Customer table:

ID        last name       Redeemed        paid
1           Cust1         10/1/16         9/15/16
2           Cust2         9/16/16         9/14/16
3           Cust3         10/4/16         9/30/16
4           Cust4         10/5/16         10/1/16

Query:

SELECT     Users.sUserName, Customers.LastName, CASE WHEN customers.Redeemed < '9/28/16' AND 
                      customers.paid < '9/28/16' THEN '3' ELSE '4' END AS Amount
FROM         Customers LEFT OUTER JOIN
                      Users ON Customers.lGreeterId = Users.ID_User
WHERE     (Customers.Redeemed BETWEEN @startdate AND @enddate)

Query output:

susername  last name      amount

Test        Cust1           4
Test2       Cust2           4
Test3       Cust3           4
Test3       Cust4           4

The conclusion should be:

susername  last name      amount

 Test        Cust1           3
 Test2       Cust2           3
 Test3       Cust3           4
 Test3       Cust4           4

Why am I getting an else result for all of them? I want to return "3" if the purchased is less than the specified date ORpaid less than the specified date.

Paid and Redeemed - Both Types of Datatype datetime

Answer 1

Following the comments, try using a different date format in the request

SELECT     Users.sUserName, Customers.LastName, 
           CASE 
             WHEN customers.Redeemed < '2016-09-28' THEN '3'
             WHEN customers.paid < '2016-09-28' THEN '3' 
             ELSE '4'
           END AS Amount
FROM         Customers 
LEFT JOIN Users 
    ON Customers.lGreeterId = Users.ID_User
WHERE     (Customers.Redeemed BETWEEN @startdate AND @enddate)