Commit d8c96f28 authored by unknown's avatar unknown
Browse files

Fixed bug #16203. 

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.
parent 26a81f6f

mysql-test/r/group_min_max.result

+27 −0
Original line number Diff line number Diff line
@@ -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;

mysql-test/t/group_min_max.test

+21 −0
Original line number Diff line number Diff line
@@ -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;

sql/opt_range.cc

+1 −0
Original line number Diff line number Diff line
@@ -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)