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Fixed bug#28404.

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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.
This commit is contained in:
igor@olga.mysql.com
2007-08-02 12:45:56 -07:00
parent 642b0c00ed
commit cf39429295
14 changed files with 359 additions and 105 deletions
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55
mysql-test/r/order_by.result
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@@ -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
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56 14
66 14
76 14
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196 14
DROP TABLE t1;