diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 21 |
1 files changed, 17 insertions, 4 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index a1f6abfd53a..92cdd12ad37 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -2688,22 +2688,35 @@ find_best(JOIN *join,table_map rest_tables,uint idx,double record_count, do { uint keypart=keyuse->keypart; - uint found_part_ref_or_null= KEY_OPTIMIZE_REF_OR_NULL; + table_map best_part_found_ref= 0; + double best_prev_record_reads= DBL_MAX; do { if (!(rest_tables & keyuse->used_tables) && !(found_ref_or_null & keyuse->optimize)) { found_part|=keyuse->keypart_map; - found_ref|= keyuse->used_tables; + double tmp= prev_record_reads(join, + (found_ref | + keyuse->used_tables)); + if (tmp < best_prev_record_reads) + { + best_part_found_ref= keyuse->used_tables; + best_prev_record_reads= tmp; + } if (rec > keyuse->ref_table_rows) rec= keyuse->ref_table_rows; - found_part_ref_or_null&= keyuse->optimize; + /* + If there is one 'key_column IS NULL' expression, we can + use this ref_or_null optimsation of this field + */ + found_ref_or_null|= (keyuse->optimize & + KEY_OPTIMIZE_REF_OR_NULL); } keyuse++; - found_ref_or_null|= found_part_ref_or_null; } while (keyuse->table == table && keyuse->key == key && keyuse->keypart == keypart); + found_ref|= best_part_found_ref; } while (keyuse->table == table && keyuse->key == key); /* |