Originally posted by DaPi
alternatively recode the IN as an EXISTS (often faster).
Actually, EXISTS is faster when you are looking in a table that has a M:n relationship with your base table.

SELECT * FROM B1 WHERE EXISTS (...L2) works best with B1 n:M L2

In this case, we are starting with the LN table and looking to the U table. Their relationship is probably LN M:1 U, so an EXISTS would, in all likelihood, not be any better.

Just an FYI,

- Chris