diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 33 |
1 files changed, 31 insertions, 2 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index ff9af8a33b9..1a29dcb62ab 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -12857,7 +12857,7 @@ remove_const(JOIN *join,ORDER *first_order, COND *cond, *simple_order=0; // Must do a temp table to sort else if (!(order_tables & not_const_tables)) { - if (order->item[0]->has_subquery()) + if (order->item[0]->with_subquery()) { /* Delay the evaluation of constant ORDER and/or GROUP expressions that @@ -12895,8 +12895,37 @@ remove_const(JOIN *join,ORDER *first_order, COND *cond, can be used without tmp. table. */ bool can_subst_to_first_table= false; + bool first_is_in_sjm_nest= false; + if (first_is_base_table) + { + TABLE_LIST *tbl_for_first= + join->join_tab[join->const_tables].table->pos_in_table_list; + first_is_in_sjm_nest= tbl_for_first->sj_mat_info && + tbl_for_first->sj_mat_info->is_used; + } + /* + Currently we do not employ the optimization that uses multiple + equalities for ORDER BY to remove tmp table in the case when + the first table happens to be the result of materialization of + a semi-join nest ( <=> first_is_in_sjm_nest == true). + + When a semi-join nest is materialized and scanned to look for + possible matches in the remaining tables for every its row + the fields from the result of materialization are copied + into the record buffers of tables from the semi-join nest. + So these copies are used to access the remaining tables rather + than the fields from the result of materialization. + + Unfortunately now this so-called 'copy back' technique is + supported only if the rows are scanned with the rr_sequential + function, but not with other rr_* functions that are employed + when the result of materialization is required to be sorted. + + TODO: either to support 'copy back' technique for the above case, + or to get rid of this technique altogether. + */ if (optimizer_flag(join->thd, OPTIMIZER_SWITCH_ORDERBY_EQ_PROP) && - first_is_base_table && + first_is_base_table && !first_is_in_sjm_nest && order->item[0]->real_item()->type() == Item::FIELD_ITEM && join->cond_equal) { |