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MDEV-25112 MIN/MAX aggregation over an indexed column may return wrong result

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If a query with implicit grouping contains in MIN/MAX set function in the
select list over a column that is a part of an index then the query
might be subject to MIN/MAX optimization. With this optimization the
server performs a look-up into an index, fetches a value of the column C
used in the MIN/MAX function and substitute the MIN/MAX expression for this
value. This allows to eliminate the table containing C from further join
processing. In order the optimization to be applied the WHERE condition
must be a conjunction of simple equality/inequality predicates or/and
BETWEEN predicates.
The bug fixed in the patch resulted in fetching a wrong value from the
index used for MIN/MAX optimization. It may happened when a BETWEEN
predicate containing the MIN/MAX value followed a strict inequality.

Approved by dmitry.shulga@mariadb.com
This commit is contained in:
Igor Babaev 2021-03-15 22:48:30 -07:00
parent c557e9540a
commit b34bb81eaf
3 changed files with 65 additions and 0 deletions
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34
mysql-test/r/func_group.result
View file

@ -2458,3 +2458,37 @@ select count(*)+sleep(0) from t1;
count(*)+sleep(0)
2
drop table t1;
#
# MDEV-25112: MIN/MAX optimization for query containing BETWEEN in WHERE
#
create table t1 (a int) engine=myisam;
insert into t1 values (267), (273), (287), (303), (308);
select max(a) from t1 where a < 303 and (a between 267 AND 287);
max(a)
287
explain select max(a) from t1 where a < 303 and (a between 267 AND 287);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 5 Using where
select min(a) from t1 where a > 267 and (a between 273 AND 303);
min(a)
273
explain select min(a) from t1 where a > 267 and (a between 273 AND 303);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 5 Using where
create index idx on t1(a);
select max(a) from t1 where a < 303 and (a between 267 AND 287);
max(a)
287
explain select max(a) from t1 where a < 303 and (a between 267 AND 287);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
select min(a) from t1 where a > 267 and (a between 273 AND 303);
min(a)
273
explain select min(a) from t1 where a > 267 and (a between 273 AND 303);
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
drop table t1;
#
# End of 10.2 tests
#

28
mysql-test/t/func_group.test
View file

@ -1703,4 +1703,32 @@ select count(*)+sleep(0) from t1;
drop table t1;
--echo #
--echo # MDEV-25112: MIN/MAX optimization for query containing BETWEEN in WHERE
--echo #
create table t1 (a int) engine=myisam;
insert into t1 values (267), (273), (287), (303), (308);
let $q1=
select max(a) from t1 where a < 303 and (a between 267 AND 287);
let $q2=
select min(a) from t1 where a > 267 and (a between 273 AND 303);
eval $q1;
eval explain $q1;
eval $q2;
eval explain $q2;
create index idx on t1(a);
eval $q1;
eval explain $q1;
eval $q2;
eval explain $q2;
drop table t1;
--echo #
--echo # End of 10.2 tests
--echo #

3
sql/opt_sum.cc
View file

@ -830,7 +830,10 @@ static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
if (is_field_part)
{
if (between || eq_type)
{
*range_fl&= ~(NO_MAX_RANGE | NO_MIN_RANGE);
*range_fl&= ~(max_fl ? NEAR_MAX : NEAR_MIN);
}
else
{
*range_fl&= ~(max_fl ? NO_MAX_RANGE : NO_MIN_RANGE);