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Fixed bug #16203.

Browse Source 
If check_quick_select returns non-empty range then the function cost_group_min_max
cannot return 0 as an estimate of the number of retrieved records.
Yet the function erroneously returned 0 as the estimate in some situations.


mysql-test/r/group_min_max.result:
  Added a test case for bug #16203.
mysql-test/t/group_min_max.test:
  Added a test case for bug #16203.
This commit is contained in:
unknown
2006-02-06 11:35:13 -08:00
parent 26a81f6fb1
commit d8c96f286f
3 changed files with 49 additions and 0 deletions
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27
mysql-test/r/group_min_max.result
View File

@ -2043,3 +2043,30 @@ c1 c2
30 8
30 9
drop table t1;
CREATE TABLE t1 (a varchar(5), b int(11), PRIMARY KEY (a,b));
INSERT INTO t1 VALUES ('AA',1), ('AA',2), ('AA',3), ('BB',1), ('AA',4);
OPTIMIZE TABLE t1;
Table Op Msg_type Msg_text
test.t1 optimize status OK
SELECT a FROM t1 WHERE a='AA' GROUP BY a;
a
AA
SELECT a FROM t1 WHERE a='BB' GROUP BY a;
a
BB
EXPLAIN SELECT a FROM t1 WHERE a='AA' GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref PRIMARY PRIMARY 7 const 3 Using where; Using index
EXPLAIN SELECT a FROM t1 WHERE a='BB' GROUP BY a;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref PRIMARY PRIMARY 7 const 1 Using where; Using index
SELECT DISTINCT a FROM t1 WHERE a='BB';
a
BB
SELECT DISTINCT a FROM t1 WHERE a LIKE 'B%';
a
BB
SELECT a FROM t1 WHERE a LIKE 'B%' GROUP BY a;
a
BB
DROP TABLE t1;

21
mysql-test/t/group_min_max.test
View File

@ -715,3 +715,24 @@ select distinct c1, c2 from t1 order by c2;
select c1,min(c2) as c2 from t1 group by c1 order by c2;
select c1,c2 from t1 group by c1,c2 order by c2;
drop table t1;
#
# Bug #16203: Analysis for possible min/max optimization erroneously
# returns impossible range
#
CREATE TABLE t1 (a varchar(5), b int(11), PRIMARY KEY (a,b));
INSERT INTO t1 VALUES ('AA',1), ('AA',2), ('AA',3), ('BB',1), ('AA',4);
OPTIMIZE TABLE t1;
SELECT a FROM t1 WHERE a='AA' GROUP BY a;
SELECT a FROM t1 WHERE a='BB' GROUP BY a;
EXPLAIN SELECT a FROM t1 WHERE a='AA' GROUP BY a;
EXPLAIN SELECT a FROM t1 WHERE a='BB' GROUP BY a;
SELECT DISTINCT a FROM t1 WHERE a='BB';
SELECT DISTINCT a FROM t1 WHERE a LIKE 'B%';
SELECT a FROM t1 WHERE a LIKE 'B%' GROUP BY a;
DROP TABLE t1;

1
sql/opt_range.cc
View File

@ -7780,6 +7780,7 @@ void cost_group_min_max(TABLE* table, KEY *index_info, uint used_key_parts,
quick_prefix_selectivity= (double) quick_prefix_records /
(double) table_records;
num_groups= (uint) rint(num_groups * quick_prefix_selectivity);
set_if_bigger(num_groups, 1);
}
if (used_key_parts > group_key_parts)