count only if field has one entry in Tableau

Question

I am using tableau and am stuck in making the field of the following code unique.

"COUNTD(
IF NOT(ISNULL([firstBillingDate]))
THEN [msisdn]
ELSE NULL
END
)"

Basically its counting unique msisdn's for all the columns which have firstbillingDate present (NOT NULL).

The problem is that one msisdn has more than one firstBillingDate. I want to count unique msidns which has only ONE firstbillingdate

Answer 1

Instead of using [firstBillingDate] in that calculation, create an LOD calc to only retrieve one date per msisdns.

{fixed [msisdns] : min([firstBillingDate]}

You can use max or min. I assumed you'd want min to return the earlier date for any multiple dates per msisdns. Now use this in your original calc.