Join Types not supported by Query Folding

[Anonymous]

Hi,

Been struggling with this for a while as there seems to be very limited documentation on Query Folding, but from what I've read it seems like all types of joins should be supported by query folding. However in practice I've found that only Left Outer joins will query fold, with all other types disabling it ( view native query is disabled and it starts downloading rows for the preview ).

I'm connecting via SQL server to our data warehouse so I can't see why this would be occuring. Currently I'm having to always use Left Outer join then expand and filter out nulls to achieve what I want which seems to be the long way round when I would like to be using inner joins.

Thanks for any help

[v-piga-msft]

Hi @Anonymous,

You could have a reference of this blog which introduces the query folding in more details.

Best Regards,

Cherry

[Anonymous]

Hi Cherry,

I have read through the blogs a few times to find the solution, but none of them I could find mention there being issues with certain join types. Can't see any mention of why a Left Outer would query fold while no others would?

Thanks,

[ImkeF · Accepted solution]

I came across this issue today as well and found a surprising solution: https://www.thebiccountant.com/2019/04/18/query-folding-joinkind-inner-gotcha-power-bi-power-query/

[Anonymous]

Hi Imke,

Sorry I only saw your reply today. It is correct though, it does Query fold at the end!. The individual step itself still doesn't though, very odd. If creating the steps one by one this was an issue as it had to download all the rows before I could continue. Not sure whether to use inner joins with this issue or continue with left join, expand and filter. Will probably need to test which returns best performance.