SQL Output Question - sql

Question

Edited
I am running into an error and I know what is happening but I can't see what is causing it. Below is the sql code I am using. Basically I am getting the general results I want, however I am not accurately giving the query the correct 'where' clause.
If this is of any assistance. The count is coming out as this:
Total Tier
1 High
2 Low
There are 4 records in the Enrollment table. 3 are active, and 1 is not. Only 2 of the records should be displayed. 1 for High, and 1 for low. The second Low record that is in the total was flagged as 'inactive' on 12/30/2010 and reflagged again on 1/12/2011 so it should not be in the results. I changed the initial '<=' to '=' and the results stayed the same.
I need to exclude any record from Enrollments_Status_Change that where the "active_status" was changed to 0 before the date.
SELECT COUNT(dbo.Enrollments.Customer_ID) AS Total,
dbo.Phone_Tier.Tier
FROM dbo.Phone_Tier as p
JOIN dbo.Enrollments as eON p.Phone_Model = e.Phone_Model
WHERE (e.Customer_ID NOT IN
(Select Customer_ID
From dbo.Enrollment_Status_Change as Status
Where (Change_Date >'12/31/2010')))
GROUP BY dbo.Phone_Tier.Tier
Thanks for any assistance and I apologize for any confusion. This is my first time here and i'm trying to correct my etiquette on the fly.

Answer 1

If you don't want any of the fields from that table dbo.Enrollment_Status_Change, and you don't seem to use it in any way — why even include it in the JOINs? Just leave it out.
Plus: start using table aliases. This is very hard to read if you use the full table name in each JOIN condition and WHERE clause.
Your code should be:
SELECT
COUNT(e.Customer_ID) AS Total, p.Tier
FROM
dbo.Phone_Tier p
INNER JOIN
dbo.Enrollments e ON p.Phone_Model = e.Phone_Model
WHERE
e.Active_Status = 1
AND EXISTS (SELECT DISTINCT Customer_ID
FROM dbo.Enrollment_Status_Change AS Status
WHERE (Change_Date <= '12/31/2010'))
GROUP BY
p.Tier
Also: most likely, your EXISTS check is wrong — since you didn't post your table structures, I can only guess — but my guess would be:
AND EXISTS (SELECT * FROM dbo.Enrollment_Status_Change
WHERE Change_Date <= '12/31/2010' AND CustomerID = e.CustomerID)
Check for existence of any entries in dbo.Enrollment_Status_Change for the customer defined by e.CustomerID, with a Change_Date before that cut-off date. Right?

Answer 2

Assuming you want to:
exclude all customers whose latest enrollment_status_change record was since the start of 2011
but
include all customers whose latest enrollment_status_change record was earlier than the end of 2010 (why else would you have put that EXISTS clause in?)
Then this should do it:
SELECT COUNT(e.Customer_ID) AS Total,
p.Tier
FROM dbo.Phone_Tier p
JOIN dbo.Enrollments e ON p.Phone_Model = e.Phone_Model
WHERE dbo.Enrollments.Active_Status = 1
AND e.Customer_ID NOT IN (
SELECT Customer_ID
FROM dbo.Enrollment_Status_Change status
WHERE (Change_Date >= '2011-01-01')
)
GROUP BY p.Tier
Basically, the problem with your code is that joining a one-to-many table will always increase the row count. If you wanted to exclude all the records that had a matching row in the other table this would be fine -- you could just use a LEFT JOIN and then set a WHERE clause like Customer_ID IS NULL.
But because you want to exclude a subset of the enrollment_status_change table, you must use a subquery.
Your intention is not clear from the example given, but if you wanted to exclude anyone who's enrollment_status_change as before 2011, but include those who's status change was since 2011, you'd just swap the date comparator for <.
Is this any help?