mirror of
https://github.com/MariaDB/server.git
synced 2025-01-27 09:14:17 +01:00
3fa99f0c0e
The main difference in code path between EQ_REF and REF is that for REF we have to do an extra read_next on the index to check that there is no more matching rows. Before this patch we added a preference of EQ_REF by ensuring that REF would always estimate to find at least 2 rows. This patch adds the cost of the extra key read_next to REF access and removes the code that limited REF to at least 2 rows. For some queries this can have a big effect as the total estimated rows will be halved for each REF table with 1 rows. multi_range cost calculations are also changed to take into account the difference between EQ_REF and REF. The effect of the patch to the test suite: - About 80 test case changed - Almost all changes where for EXPLAIN where estimated rows for REF where changed from 2 to 1. - A few test cases using explain extended had a change of 'filtered'. This is because of the estimated rows are now closer to the calculated selectivity. - A very few test had a change of table order. This is because the change of estimated rows from 2 to 1 or the small cost change for REF (main.subselect_sj_jcl6, main.group_by, main.dervied_cond_pushdown, main.distinct, main.join_nested, main.order_by, main.join_cache) - No key statistics and the estimated rows are now smaller which cased estimated filtering to be lower. (main.subselect_sj_mat) - The number of total rows are halved. (main.derived_cond_pushdown) - Plans with 1 row changed to use RANGE instead of REF. (main.group_min_max) - ALL changed to REF (main.key_diff) - Key changed from ref + index_only to PRIMARY key for InnoDB, as OPTIMIZER_ROW_LOOKUP_COST + OPTIMIZER_ROW_NEXT_FIND_COST is smaller than OPTIMIZER_KEY_LOOKUP_COST + OPTIMIZER_KEY_NEXT_FIND_COST. (main.join_outer_innodb) - Cost changes printouts (main.opt_trace*) - Result order change (innodb_gis.rtree)
52 lines
819 B
Text
52 lines
819 B
Text
drop table if exists t1;
|
|
CREATE TABLE t1 (
|
|
a char(5) NOT NULL,
|
|
b char(4) NOT NULL,
|
|
KEY (a),
|
|
KEY (b)
|
|
);
|
|
INSERT INTO t1 VALUES ('A','B'),('b','A'),('C','c'),('D','E'),('a','a');
|
|
select * from t1,t1 as t2;
|
|
a b a b
|
|
A B A B
|
|
b A A B
|
|
C c A B
|
|
D E A B
|
|
a a A B
|
|
A B b A
|
|
b A b A
|
|
C c b A
|
|
D E b A
|
|
a a b A
|
|
A B C c
|
|
b A C c
|
|
C c C c
|
|
D E C c
|
|
a a C c
|
|
A B D E
|
|
b A D E
|
|
C c D E
|
|
D E D E
|
|
a a D E
|
|
A B a a
|
|
b A a a
|
|
C c a a
|
|
D E a a
|
|
a a a a
|
|
explain select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B;
|
|
id select_type table type possible_keys key key_len ref rows Extra
|
|
1 SIMPLE t1 ALL a NULL NULL NULL 5
|
|
1 SIMPLE t2 ref b b 4 test.t1.a 1 Using index condition
|
|
select t1.*,t2.* from t1,t1 as t2 where t1.A=t2.B order by binary t1.a,t2.a;
|
|
a b a b
|
|
A B a a
|
|
A B b A
|
|
C c C c
|
|
a a a a
|
|
a a b A
|
|
b A A B
|
|
select * from t1 where a='a';
|
|
a b
|
|
A B
|
|
a a
|
|
drop table t1;
|