How do I combine custom SQL across databases into a single table?

Hi Believer 

Based on my test, you can try the following code. Sql.Database - PowerQuery M

let
    CustomSQL = "SELECT * FROM Table_1 WHERE Provider='a';",
    Table1 = Sql.Database("SQLServer1", "Database1", [Query=CustomSQL]),
    Table2 = Sql.Database("SQLServer2", "Database2", [Query=CustomSQL]),
    Source = Table.Combine({Table1, Table2})
in
    Source

Best Regards,
Community Support Team _ Jing
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