Same result with or without RELATEDTABLE

[tiptran]

Hi, 

I am referring to the RELATEDTABLE example in https://docs.microsoft.com/en-us/dax/relatedtable-function-dax

Internet Sales = SUMX( RELATEDTABLE('InternetSales_USD') , [SalesAmount_USD])

Since the 'Product Category' table is linked to 'InternetSales_USD' table in a relationship (1 to many), I found that the following DAX would return the same result as the above: 

Internet Sales = SUM( 'InternetSales_USD' [SalesAmount_USD])

What is the point of having RELATEDTABLE when the same result could be obtained without it? I know that Tableau does not require explicit command such as RELATEDTABLE to retrieve data from another joined table. You can simply define the relationship (with correct cardinality) and the program would pull the related data for you without any problem.

Thanks

[Mariusz]

Hi @tiptran 

If you are creating Measure then the result would be the same, however, it would differ when creating a Column, in such scenario RELATEDTABLE or CALCULATE is necessary to preform context transition.
https://www.sqlbi.com/articles/understanding-context-transition/

Best Regards,
Mariusz

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[tiptran]

Thank you, Mariusz. Could you explain why the result is the same if the following formula is used to create a measure and it differs for a new column? 

Internet Sales = SUM( 'InternetSales_USD' [SalesAmount_USD])

I am guessing that:

• for a measure, the formula is dynamic enough so that it is responsive to visual's context, i.e. it aggregates sales for each product category (each row)
• For a column, the formula does not take into account what attributes are present in the visual, and hence blindly aggregating everything from the InternetSales_USD table. 

Am I right?

Thanks again

[Mariusz · Accepted solution]

Hi @tiptran 

Measures will implicitly apply a CALCULATE around every statement, so if you create a Measure 

Measure = SUM( sales[Sales Amt] )

in reality, this will be  

Measure = CALCULATE( SUM( sales[Sales Amt] ) )

and CALCULATE performs context transition so RELATEDTABLE is not necessary.

Please read the link that you have posted explaining RELATEDTABLE and the one that I have and you should be able to understand.

Best Regards,
Mariusz

If this post helps, then please consider Accepting it as the solution.

Please feel free to connect with me.
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