I have uploaded an example document presented below as well as a snipp of it.
Issue Example Excel file
Below is the formula i tried using in column E of the example file, it works well on small tables but the one my query generets is 100k+ lines, with the lookup table being 40k+ lines.
=IFERROR(INDEX(Lookup_Table[Sales Rep],MATCH(1,(Lookup_Table[Account ID]=[@AccountID])*(Lookup_Table[Assignment start month year]<=[@YearMonth])*(Lookup_Table[Assignment End Month Year]>=[@YearMonth]),0)),"Account not Assigned")
Hope this helps.
Thank you for taking a look into this, hope i will in the future 🙂