diff options
Diffstat (limited to 'sql/opt_subselect.cc')
| -rw-r--r-- | sql/opt_subselect.cc | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/sql/opt_subselect.cc b/sql/opt_subselect.cc index 56b76f5982e..9bf1aaf4039 100644 --- a/sql/opt_subselect.cc +++ b/sql/opt_subselect.cc @@ -5467,8 +5467,8 @@ bool JOIN::choose_tableless_subquery_plan() /* If the optimizer determined that his query has an empty result, in most cases the subquery predicate is a known constant value - - either FALSE or NULL. The implementation of Item_subselect::reset() - determines which one. + either of TRUE, FALSE or NULL. The implementation of + Item_subselect::no_rows_in_result() determines which one. */ if (zero_result_cause) { @@ -5476,14 +5476,13 @@ bool JOIN::choose_tableless_subquery_plan() { /* Both group by queries and non-group by queries without aggregate - functions produce empty subquery result. + functions produce empty subquery result. There is no need to further + rewrite the subquery because it will not be executed at all. */ - subs_predicate->reset(); - subs_predicate->make_const(); return FALSE; } - /* TODO: + /* @todo A further optimization is possible when a non-group query with MIN/MAX/COUNT is optimized by opt_sum_query. Then, if there are only MIN/MAX functions over an empty result set, the subquery |