Skip to content
Permalink
Browse files

Fixed bug#28404.

This patch adds cost estimation for the queries with ORDER BY / GROUP BY
and LIMIT. 
If there was a ref/range access to the table whose rows were required
to be ordered in the result set the optimizer always employed this access
though a scan by a different index that was compatible with the required 
order could be cheaper to produce the first L rows of the result set.
Now for such queries the optimizer makes a choice between the cheapest
ref/range accesses not compatible with the given order and index scans
compatible with it.
  • Loading branch information...
igor@olga.mysql.com
igor@olga.mysql.com committed Aug 2, 2007
1 parent 642b0c0 commit cf39429295846cf944e3fd1a327c554ebd08942d
@@ -209,16 +209,16 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 4 Using index
explain SELECT distinct t1.a from t1 order by a desc limit 1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL 4 Using index
1 SIMPLE t1 index NULL PRIMARY 4 NULL 1 Using index
explain SELECT distinct a from t3 order by a desc limit 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 index NULL a 5 NULL 204 Using index
1 SIMPLE t3 index NULL a 5 NULL 40 Using index
explain SELECT distinct a,b from t3 order by a+1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 ALL NULL NULL NULL NULL 204 Using temporary; Using filesort
explain SELECT distinct a,b from t3 order by a limit 10;
explain SELECT distinct a,b from t3 order by a limit 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 index NULL a 5 NULL 204 Using temporary
1 SIMPLE t3 index NULL a 5 NULL 2 Using temporary
explain SELECT a,b from t3 group by a,b order by a+1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 ALL NULL NULL NULL NULL 204 Using temporary; Using filesort
@@ -154,7 +154,7 @@ teststring
teststring
explain select * from t1 order by text1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL key1 34 NULL 3
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using filesort
alter table t1 modify text1 char(32) binary not null;
select * from t1 order by text1;
text1
@@ -1144,7 +1144,7 @@ CREATE TABLE t2 (a INT, b INT, KEY(a));
INSERT INTO t2 VALUES (1, 1), (2, 2), (3,3), (4,4);
EXPLAIN SELECT a, SUM(b) FROM t2 GROUP BY a LIMIT 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 index NULL a 5 NULL 4
1 SIMPLE t2 index NULL a 5 NULL 2
EXPLAIN SELECT a, SUM(b) FROM t2 IGNORE INDEX (a) GROUP BY a LIMIT 2;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t2 ALL NULL NULL NULL NULL 4 Using temporary; Using filesort
@@ -1963,20 +1963,20 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 128 Using temporary; Using filesort
explain select a1,a2,count(a2) from t1 group by a1,a2,b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL idx_t1_1 163 NULL 128 Using index
1 SIMPLE t1 index NULL idx_t1_2 147 NULL 128 Using index
explain extended select a1,a2,count(a2) from t1 where (a1 > 'a') group by a1,a2,b;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 index idx_t1_0,idx_t1_1,idx_t1_2 idx_t1_1 163 NULL 128 75.00 Using where; Using index
1 SIMPLE t1 index idx_t1_0,idx_t1_1,idx_t1_2 idx_t1_2 147 NULL 128 75.00 Using where; Using index
Warnings:
Note 1003 select `test`.`t1`.`a1` AS `a1`,`test`.`t1`.`a2` AS `a2`,count(`test`.`t1`.`a2`) AS `count(a2)` from `test`.`t1` where (`test`.`t1`.`a1` > _latin1'a') group by `test`.`t1`.`a1`,`test`.`t1`.`a2`,`test`.`t1`.`b`
explain extended select sum(ord(a1)) from t1 where (a1 > 'a') group by a1,a2,b;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t1 index idx_t1_0,idx_t1_1,idx_t1_2 idx_t1_1 163 NULL 128 75.00 Using where; Using index
1 SIMPLE t1 index idx_t1_0,idx_t1_1,idx_t1_2 idx_t1_2 147 NULL 128 75.00 Using where; Using index
Warnings:
Note 1003 select sum(ord(`test`.`t1`.`a1`)) AS `sum(ord(a1))` from `test`.`t1` where (`test`.`t1`.`a1` > _latin1'a') group by `test`.`t1`.`a1`,`test`.`t1`.`a2`,`test`.`t1`.`b`
explain select distinct(a1) from t1 where ord(a2) = 98;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL idx_t1_1 163 NULL 128 Using where; Using index
1 SIMPLE t1 index NULL idx_t1_2 147 NULL 128 Using where; Using index
select distinct(a1) from t1 where ord(a2) = 98;
a1
a
@@ -2256,7 +2256,7 @@ EXPLAIN SELECT 1 FROM t1 AS t1_outer WHERE
a IN (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1_outer index NULL a 10 NULL 15 Using where; Using index
2 DEPENDENT SUBQUERY t1 index NULL a 10 NULL 15 Using index
2 DEPENDENT SUBQUERY t1 index NULL a 10 NULL 1 Using index
EXPLAIN SELECT 1 FROM t1 AS t1_outer GROUP BY a HAVING
a > (SELECT max(b) FROM t1 GROUP BY a HAVING a < 2);
id select_type table type possible_keys key key_len ref rows Extra
@@ -947,7 +947,7 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL PRIMARY 4 NULL #
explain select * from t1 order by b;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL b 4 NULL #
1 SIMPLE t1 ALL NULL NULL NULL NULL # Using filesort
explain select * from t1 order by c;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL # Using filesort
@@ -851,13 +851,13 @@ EXPLAIN SELECT * FROM t1 WHERE b BETWEEN 1 AND 2 ORDER BY a;
id 1
select_type SIMPLE
table t1
type range
type index
possible_keys bkey
key bkey
key_len 5
key PRIMARY
key_len 4
ref NULL
rows 16
Extra Using where; Using index; Using filesort
rows 32
Extra Using where; Using index
SELECT * FROM t1 WHERE b BETWEEN 1 AND 2 ORDER BY a;
a b
1 2
@@ -946,13 +946,13 @@ EXPLAIN SELECT * FROM t2 WHERE b=1 ORDER BY a;
id 1
select_type SIMPLE
table t2
type ref
type index
possible_keys bkey
key bkey
key_len 5
ref const
rows 8
Extra Using where; Using index; Using filesort
key PRIMARY
key_len 4
ref NULL
rows 16
Extra Using where; Using index
SELECT * FROM t2 WHERE b=1 ORDER BY a;
a b c
1 1 1
@@ -86,7 +86,7 @@ a b
19 Testing
explain select a from t3 order by a desc limit 10;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t3 index NULL a 4 NULL 1131 Using index
1 SIMPLE t3 index NULL a 4 NULL 10 Using index
select a from t3 order by a desc limit 10;
a
699
@@ -1073,3 +1073,58 @@ id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 const PRIMARY,b b 5 const 1
1 SIMPLE t2 ref a a 5 const 2 Using where; Using index
DROP TABLE t1,t2;
CREATE TABLE t1(
id int auto_increment PRIMARY KEY, c2 int, c3 int, INDEX k2(c2), INDEX k3(c3));
INSERT INTO t1 (c2,c3) VALUES
(31,34),(35,38),(34,31),(32,35),(31,39),
(11,14),(15,18),(14,11),(12,15),(11,19);
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
SELECT COUNT(*) FROM t1;
COUNT(*)
40960
EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index k2 k3 5 NULL 88 Using where
EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref k2 k2 5 const 9300 Using where; Using filesort
EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 100;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index k2 k3 5 NULL 316 Using where
EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 2000;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range k2 k2 5 NULL 12937 Using where; Using filesort
SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
id c3
6 14
16 14
26 14
36 14
46 14
56 14
66 14
76 14
86 14
96 14
106 14
116 14
126 14
136 14
146 14
156 14
166 14
176 14
186 14
196 14
DROP TABLE t1;
@@ -84,7 +84,7 @@ UNIQUE KEY e_n (email,name)
EXPLAIN SELECT SQL_CALC_FOUND_ROWS DISTINCT email FROM t2 LEFT JOIN t1 ON kid = t2.id WHERE t1.id IS NULL LIMIT 10;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 system PRIMARY,kid NULL NULL NULL 0 const row not found
1 SIMPLE t2 index NULL e_n 104 NULL 200
1 SIMPLE t2 index NULL e_n 104 NULL 10
SELECT SQL_CALC_FOUND_ROWS DISTINCT email FROM t2 LEFT JOIN t1 ON kid = t2.id WHERE t1.id IS NULL LIMIT 10;
email
email1
@@ -3419,7 +3419,7 @@ EXPLAIN
SELECT * FROM t1 WHERE (a,b) = ANY (SELECT a, max(b) FROM t1 GROUP BY a);
id select_type table type possible_keys key key_len ref rows Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 9 Using where
2 DEPENDENT SUBQUERY t1 index NULL a 8 NULL 9 Using filesort
2 DEPENDENT SUBQUERY t1 index NULL a 8 NULL 1 Using filesort
DROP TABLE t1;
create table t1( f1 int,f2 int);
insert into t1 values (1,1),(2,2);
@@ -97,7 +97,7 @@ explain SELECT t1.a from t1 group by a order by a desc;
explain SELECT distinct t1.a from t1 order by a desc limit 1;
explain SELECT distinct a from t3 order by a desc limit 2;
explain SELECT distinct a,b from t3 order by a+1;
explain SELECT distinct a,b from t3 order by a limit 10;
explain SELECT distinct a,b from t3 order by a limit 2;
explain SELECT a,b from t3 group by a,b order by a+1;

drop table t1,t2,t3,t4;
@@ -739,3 +739,40 @@ INSERT INTO t2 VALUES (1,1),(1,2),(2,1),(2,2);
EXPLAIN SELECT 1 FROM t1,t2 WHERE t1.b=2 AND t1.a=t2.a ORDER BY t2.b;

DROP TABLE t1,t2;

# End of 5.0

#
# Bug #28404: query with ORDER BY and ref access
#

CREATE TABLE t1(
id int auto_increment PRIMARY KEY, c2 int, c3 int, INDEX k2(c2), INDEX k3(c3));

INSERT INTO t1 (c2,c3) VALUES
(31,34),(35,38),(34,31),(32,35),(31,39),
(11,14),(15,18),(14,11),(12,15),(11,19);

INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;
INSERT INTO t1 (c2,c3) SELECT c2,c3 FROM t1;

SELECT COUNT(*) FROM t1;

EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;
EXPLAIN SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 100;
EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 100;
EXPLAIN SELECT id,c3 FROM t1 WHERE c2 BETWEEN 10 AND 12 ORDER BY c3 LIMIT 2000;

SELECT id,c3 FROM t1 WHERE c2=11 ORDER BY c3 LIMIT 20;

DROP TABLE t1;

0 comments on commit cf39429

Please sign in to comment.
You can’t perform that action at this time.