Tender,
not sure you see one suggestion i did.
just in case you think it may be interesting, i modified for you 0001.
it just add (and reindent) ' if(forced_null_vars != NIL) ' around the
optimisation while most of left join have probably no forced nulls,
and thus it avoids to compute find_nonnullable_vars and
have_var_is_notnull for them.
Nicolas