SQl apply where clause to only one field - sql

Question

I'd like to apply a WHERE clause to just one field of my select query. The internet told me to use CASE WHEN in the line where I'm selecting my fields and to then remove the where clause. But I was then told that my "selected non aggregate values must be part of the associated group."
The original query looked like this:
SELECT
CAST(EVENT_TIMESTAMP AS DATE) AS Date1,
COUNT(DISTINCT EMAIL) END AS Subs,
SUM(DWELL_MINUTES) AS Dwell
FROM VwNIMEventFct
INNER JOIN VwNIMUserDim ON VwNIMUserDim.NIM_USER_ID = VwNIMEventFct.NIM_USER_ID
INNER JOIN TmpNIMSalesForceDB ON VwNIMUserDim.USER_EMAIL_ADDRESS = EMAIL
WHERE Date1 >= '2013-11-01'
// The problem is here, in the AND clause
AND (SUBSCRIPTION_END_DATE > VwNIMEventFct.EVENT_TIMESTAMP OR SUBSCRIPTION_END_DATE
IS NULL)
GROUP BY Date1
ORDER BY Date1
I then changed the query after doing some searching to this:
SELECT
CAST(EVENT_TIMESTAMP AS DATE) AS Date1,
CASE WHEN (SUBSCRIPTION_END_DATE > Date1 OR SUBSCRIPTION_END_DATE IS NULL)
THEN COUNT(DISTINCT TmpNIMSalesForceDB.EMAIL) END AS Subs,
SUM(VwNIMEventFct.DWELL_MINUTES) AS Dwell
FROM RDMAVWSANDBOX.VwNIMEventFct
INNER JOIN VwNIMUserDim ON VwNIMUserDim.NIM_USER_ID = VwNIMEventFct.NIM_USER_ID
INNER JOIN TmpNIMSalesForceDB ON VwNIMUserDim.USER_EMAIL_ADDRESS = EMAIL
WHERE Date1 >= '2013-11-01'
GROUP BY Date1
ORDER BY Date1
I'd like to select:
1) the date as per "Date1" in the query, then,
2) for each date, the count of distinct email addresses where the SUBSCRIPTION_END_DATE is either NULL or in the future (greater than Date1),
3) Sum of a field (I'm fine here)
How do I do number 2?
EDIT based on answer:
Does this part of the select query ignore and thus not count blank records when
SUBSCRIPTION_END_DATE is null?
SELECT
COUNT(DISTINCT CASE WHEN TmpNIMSalesForceDB.SUBSCRIPTION_END_DATE > Date1 OR TmpNIMSalesForceDB.SUBSCRIPTION_END_DATE IS NULL
THEN TmpNIMSalesForceDB.EMAIL END) AS Subs,
I need to count all records where SUBSCRIPTION_END_DATE is blank/null or where those dates are after Date1.

Answer 1

You need to put your CASE statement inside the COUNT, rather than vice versa, as it needs to be evaluated for each row (which case should this row fall in) and then aggregated across each group (how many rows in that group fell in the non-null group).
COUNT(DISTINCT CASE WHEN (SUBSCRIPTION_END_DATE > Date1 OR SUBSCRIPTION_END_DATE IS NULL)
THEN TmpNIMSalesForceDB.EMAIL END) AS Subs
The COUNT will ignore the NULLs implicitly left by the lack of an ELSE clause in the CASE statement, thus counting only the distinct EMAIL values from rows which met the condition.

Answer 2

Put the case statement inside of the count function.
SELECT
CAST(EVENT_TIMESTAMP AS DATE) AS Date1,
COUNT(DISTINCT(CASE
WHEN SUBSCRIPTION_END_DATE > Date1 OR SUBSCRIPTION_END_DATE IS NULL
THEN TmpNIMSalesForceDB.EMAIL END)) AS Subs,
SUM(VwNIMEventFct.DWELL_MINUTES) AS Dwell
FROM RDMAVWSANDBOX.VwNIMEventFct
INNER JOIN VwNIMUserDim
ON VwNIMUserDim.NIM_USER_ID = VwNIMEventFct.NIM_USER_ID
INNER JOIN TmpNIMSalesForceDB
ON VwNIMUserDim.USER_EMAIL_ADDRESS = EMAIL
WHERE Date1 >= '2013-11-01'
GROUP BY Date1
ORDER BY Date1