Late NULLs Filtering

Suppose we have a query plan with table tblX being accessed via the ref access method:

tblX.key_part1 = expr1 AND tblX.key_part2 = expr2 AND ...

Before performing an index lookup, we determine whether any of the expri values is NULL. If it is, we don't perform the lookup, but rather immediately return that the matching tuple is not found.

This optimization reuses the null_rejecting attribute produced by the early NULLs filtering code (see Section, “Early NULLs Filtering”). The check itself is located in the function join_read_always_key().