database/mariadb
1
0
Fork 0
mirror of https://github.com/MariaDB/server.git synced 2025-07-29 05:21:33 +03:00
Code Activity

Bug #41610: key_infix_len can be overwritten causing some group by queries to

Browse Source 
return no rows

The algorithm of determining the best key for loose index scan is doing a loop
over the available indexes and selects the one that has the best cost.
It retrieves the parameters of the current index into a set of variables.
If the cost of using the current index is lower than the best cost so far it 
copies these variables into another set of variables that contain the 
information for the best index so far.
After having checked all the indexes it uses these variables (outside of the 
index loop) to create the table read plan object instance.
The was a single omission : the key_infix/key_infix_len variables were used 
outside of the loop without being preserved in the loop for the best index 
so far.
This causes these variables to get overwritten by the next index(es) checked.
Fixed by adding variables to hold the data for the current index, passing 
the new variables to the function that assigns values to them and copying 
the new variables into the existing ones when selecting a new current best 
index.
To avoid further such problems moved the declarations of the variables used 
to keep information about the current index inside the loop's compound 
statement.
This commit is contained in:
Georgi Kodinov
2009-02-27 15:25:06 +02:00
parent fb78405625
commit 4d2f047e95
3 changed files with 70 additions and 25 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
mysql-test/r/group_min_max.result
View File

@ -2429,3 +2429,18 @@ id select_type table type possible_keys key key_len ref rows Extra
Warnings:
Note 1003 select sql_buffer_result `test`.`t1`.`a` AS `a`,(max(`test`.`t1`.`b`) + 1) AS `max(b)+1` from `test`.`t1` where (`test`.`t1`.`a` = 0) group by `test`.`t1`.`a`
drop table t1;
CREATE TABLE t1 (a int, b int, c int, d int,
KEY foo (c,d,a,b), KEY bar (c,a,b,d));
INSERT INTO t1 VALUES (1, 1, 1, 1), (1, 1, 1, 2), (1, 1, 1, 3), (1, 1, 1, 4);
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT a,b,c+1,d FROM t1;
EXPLAIN SELECT DISTINCT c FROM t1 WHERE d=4;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 range NULL foo 10 NULL 9 Using where; Using index for group-by
SELECT DISTINCT c FROM t1 WHERE d=4;
c
1
2
DROP TABLE t1;
End of 5.0 tests

23
mysql-test/t/group_min_max.test
View File

@ -935,3 +935,26 @@ insert into t1 (a,b) select a, max(b)+1 from t1 where a = 0 group by a;
select * from t1;
explain extended select sql_buffer_result a, max(b)+1 from t1 where a = 0 group by a;
drop table t1;
#
# Bug #41610: key_infix_len can be overwritten causing some group by queries
# to return no rows
#
CREATE TABLE t1 (a int, b int, c int, d int,
KEY foo (c,d,a,b), KEY bar (c,a,b,d));
INSERT INTO t1 VALUES (1, 1, 1, 1), (1, 1, 1, 2), (1, 1, 1, 3), (1, 1, 1, 4);
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT * FROM t1;
INSERT INTO t1 SELECT a,b,c+1,d FROM t1;
#Should be non-empty
--ordered_result
EXPLAIN SELECT DISTINCT c FROM t1 WHERE d=4;
SELECT DISTINCT c FROM t1 WHERE d=4;
DROP TABLE t1;
--echo End of 5.0 tests