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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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2
mysql-test/r/endspace.result
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@@ -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