let
    Source = Sql.Database("(localdb)\MSSQLLocalDB", "DAX", [Query=
"
Begin Transaction;
If (Object_Id(N'tempdb..#external', N'U') Is Not Null) Drop Table #external;
Create Table #external (fid int, fname nvarchar(5));
Insert Into #external (fid, fname)
Values 
(1, N'name1'), (2, N'name2'),
(3, N'name3'), (4, N'name4');
Insert Into dbo.test_table (fid, fname) 
Select tsrc.fid, tsrc.fname 
From #external tsrc
Left Join dbo.test_table tdest On (tsrc.fid = tdest.fid)
Where tdest.fid Is Null; 
Commit Transaction;
"])
in
    Source