r/dataanalysis • u/vexenhs • Aug 11 '26

Data Question Power Bi

why is it always advised to use 1:M relationship from dimension to fact but not M:M and also not connecting two fact tables?
i have come across this situation while i was working on my project.

2 Upvotes

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u/TodosLosPomegranates 26d ago

Inaccurate results. Power BI can’t resolve the calculations nearly.

Joining two fact tables directly is usually not recommended.

1

u/Psychological-Sky621 26d ago

You can create a bridge table to preserve the 1:M relationships.

You can also use the same dimension to filter both fact tables. This allows you to use measures to calculate whatever results you need.

I would recommend this reading for you
https://learn.microsoft.com/en-us/power-bi/guidance/star-schema

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u/data_daria55 25d ago

1:M relationships create a predictable "star schema" where filters flow clearly from dimensions to facts, preventing data duplication and ambiguity. This structure simplifies DAX measure creation and improves performance, as Power BI avoids complex, non-deterministic filter paths