LastDate and FirstDate

[Anonymous]

Hi,

when we use these two functions, i know it's gonna apply to all the data if there is no data applicable. 

FIRSTDATE(DATEADD('leads final'[modifiedon (bins)], -12, MONTH)) when i use this functio, if the last year is not available, how can i avoid it to select all the dates? instead, i want it to leave as blank/NA

any good ideas? 

[Anonymous]

Hi there.

First of all, you should read this: https://dax.guide/firstdate/ and when you do, please read it WELL with full attention to the DETAILS.

Secondly, you should be aware that FIRSTDATE is a table function that returns a TABLE, not a value (even though it can be automatically converted into a value on demand).

Thirdly, you should use this function only on A PROPER DATE TABLE. Same is (even more) true for DATEADD. If you don't follow the rules, then you'll be sorry rather sooner than later 🙂 Please mark my words well.

FIRSTDATE returns the very first date in the column passed in as the parameter. DATEADD shifts a column by the desired amount of time BUT ONLY IF the shifted period is present in the passed-in column. If not, then BLANK will be returned and hence all other time-related functions will return BLANK. Let me warn you again: DO NOT USE TIME-INTELLIGENCE FUNCTIONS ON NON-DATE TABLES.

Best

Darek