diff options
Diffstat (limited to 'sql/sql_select.cc')
| -rw-r--r-- | sql/sql_select.cc | 47 |
1 files changed, 32 insertions, 15 deletions
diff --git a/sql/sql_select.cc b/sql/sql_select.cc index 0fbc4bac7d8..13a5cd88c93 100644 --- a/sql/sql_select.cc +++ b/sql/sql_select.cc @@ -5507,18 +5507,16 @@ add_key_field(JOIN *join, (*key_fields)->level= and_level; (*key_fields)->optimize= optimize; /* - If the condition has form "tbl.keypart = othertbl.field" and - othertbl.field can be NULL, there will be no matches if othertbl.field - has NULL value. - We use null_rejecting in add_not_null_conds() to add - 'othertbl.field IS NOT NULL' to tab->select_cond. + If the condition we are analyzing is NULL-rejecting and at least + one side of the equalities is NULLable, mark the KEY_FIELD object as + null-rejecting. This property is used by: + - add_not_null_conds() to add "column IS NOT NULL" conditions + - best_access_path() to produce better estimates for NULL-able unique keys. */ { - Item *real= (*value)->real_item(); - if (((cond->functype() == Item_func::EQ_FUNC) || - (cond->functype() == Item_func::MULT_EQUAL_FUNC)) && - (real->type() == Item::FIELD_ITEM) && - ((Item_field*)real)->field->maybe_null()) + if ((cond->functype() == Item_func::EQ_FUNC || + cond->functype() == Item_func::MULT_EQUAL_FUNC) && + ((*value)->maybe_null || field->real_maybe_null())) (*key_fields)->null_rejecting= true; else (*key_fields)->null_rejecting= false; @@ -6834,6 +6832,7 @@ best_access_path(JOIN *join, ulong key_flags; uint key_parts; key_part_map found_part= 0; + key_part_map notnull_part=0; // key parts which won't have NULL in lookup tuple. table_map found_ref= 0; uint key= keyuse->key; bool ft_key= (keyuse->keypart == FT_KEYPART); @@ -6892,6 +6891,9 @@ best_access_path(JOIN *join, if (!(keyuse->used_tables & ~join->const_table_map)) const_part|= keyuse->keypart_map; + if (!keyuse->val->maybe_null || keyuse->null_rejecting) + notnull_part|=keyuse->keypart_map; + double tmp2= prev_record_reads(join->positions, idx, (found_ref | keyuse->used_tables)); if (tmp2 < best_prev_record_reads) @@ -6942,12 +6944,19 @@ best_access_path(JOIN *join, loose_scan_opt.check_ref_access_part1(s, key, start_key, found_part); /* Check if we found full key */ - if (found_part == PREV_BITS(uint, key_parts) && - !ref_or_null_part) + const key_part_map all_key_parts= PREV_BITS(uint, key_parts); + if (found_part == all_key_parts && !ref_or_null_part) { /* use eq key */ max_key_part= (uint) ~0; - if ((key_flags & (HA_NOSAME | HA_NULL_PART_KEY)) == HA_NOSAME || - MY_TEST(key_flags & HA_EXT_NOSAME)) + /* + If the index is a unique index (1), and + - all its columns are not null (2), or + - equalities we are using reject NULLs (3) + then the estimate is rows=1. + */ + if ((key_flags & (HA_NOSAME | HA_EXT_NOSAME)) && // (1) + (!(key_flags & HA_NULL_PART_KEY) || // (2) + all_key_parts == notnull_part)) // (3) { tmp = prev_record_reads(join->positions, idx, found_ref); records=1.0; @@ -9991,8 +10000,16 @@ static bool create_ref_for_key(JOIN *join, JOIN_TAB *j, uint maybe_null= MY_TEST(keyinfo->key_part[i].null_bit); j->ref.items[i]=keyuse->val; // Save for cond removal j->ref.cond_guards[i]= keyuse->cond_guard; - if (keyuse->null_rejecting) + + /* + Set ref.null_rejecting to true only if we are going to inject a + "keyuse->val IS NOT NULL" predicate. + */ + Item *real= (keyuse->val)->real_item(); + if (keyuse->null_rejecting && (real->type() == Item::FIELD_ITEM) && + ((Item_field*)real)->field->maybe_null()) j->ref.null_rejecting|= (key_part_map)1 << i; + keyuse_uses_no_tables= keyuse_uses_no_tables && !keyuse->used_tables; /* We don't want to compute heavy expressions in EXPLAIN, an example would |