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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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6
sql/sql_select.h
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@ -194,6 +194,12 @@ typedef struct st_join_table {
enum join_type type;
bool cached_eq_ref_table,eq_ref_table,not_used_in_distinct;
bool sorted;
/*
If it's not 0 the number stored this field indicates that the index
scan has been chosen to access the table data and we expect to scan
this number of rows for the table.
*/
ha_rows limit;
TABLE_REF ref;
JOIN_CACHE cache;
JOIN *join;