Forum Discussion
Power query merge vs SQL joins
If connecting directly to SQL Server it may not matter as a merge in Power Query gets folded back to the server so the server does the join and merge. But if you are going through an ODBC driver, or using a data source that doesn't fold, then you definitely want to do the merge in the source database.
The general rule is push tranformations back as far to the source as possible, but do them as late as is necessary. So if you have the option to do the merge in SQL and present a view to Power Query, do it.
From functional perspective, the most impactful restriction of PQ joins is that PQ, so far is limited to the equality of the values of the key columns; that's to say, you can't join tables by
Table1 (INNER/LEFT/RIGHT/...) JOIN Table2 ON Table1.Col1 >= Table2.Col2
From performance perspective, as far as I know, "traditional" databases joins are way more performant then PQ.