ALLSELECTED and CALCULATE inside SUMX vs plain CALCULATE

[Han_Solo]

Hello,

while working on one report I've encountered two measures that I do not quite understand. 

Here's the sample of the data:

https://we.tl/t-Lgp69wQDVN

In general it looks like that and it goes with date (end of week) and Customer_ID

This measure just counts the distinct values of Customer_ID dependent by the context. 

Unique_Customer_Simple = CALCULATE( DISTINCTCOUNT('dataset'[Customer_ID]))

This one, counts the distinct values of Customer_ID but taking down the context filter of date but keeping the outside filters. So for example if we would set month filter on only april and in matrix we would have only date column, it would show us total sum of distinct values of april for every date, do I get it right?

Unique_Customer_2 = CALCULATE( 
 DISTINCTCOUNT('dataset'[Customer_ID]), 
  ALLSELECTED('dataset'[Date] )
)

But what does this measure do? What is the difference between the above? I tried to play with it and it shows completely different values with CALCULATE inside the SUMX and without it. 

Unique_Customer_3 = 
VAR Total = SUMX( ALLSELECTED('dataset'[Date] ),
                    CALCULATE(DISTINCTCOUNT('dataset'[Customer_ID])))
RETURN Total

Thank you for help

Best Regards 

[Han_Solo · Accepted solution]

IF anyone still wound be interested - 
mostly I needed to read 
https://www.sqlbi.com/articles/the-definitive-guide-to-allselected/
and ALLSELECTED solutions from Definitive Guide to DAX. previous answers are mostly not useful at all. In general it's mostly about shadow context and how ALLSELECTED changes the context because of it's natural behavior. best would be to work on that personally but link will help a lot. 

[v-yiruan-msft]

Hi @Han_Solo ,

Please review the following blog, hope it can help you can get a good understanding about CALCULATE and ALLSELECTED function.

How CALCULATE works in DAX

The definitive guide to ALLSELECTED

Best Regards
Community Support Team _ Rena Ruan
If this post helps, then please consider Accept it as the solution to help the other members find it more.

[amitchandak]

@Han_Solo , refer the execution difference

https://radacad.com/sum-vs-sumx-what-is-the-difference-of-the-two-dax-functions-in-power-bi

[Han_Solo]

Sorry but that's not helpful. I understand the difference between sum and sumx. I just don't understand behaviour of allcalculated there.