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MDEV-20773 Error from UPDATE when estimating selectivity of a range

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This bug could affect multi-update statements as well as single-table
update statements processed as multi-updates when the where condition
contained a range condition over a non-indexed varchar column. The
optimizer calculates selectivity of such range conditions using histograms.
For each range the buckets containing endpoints of the the range are
determined with a procedure that stores the values of the endpoints in the
space of the record buffer where values of the columns are usually stored.
For a range over a varchar column the value of a endpoint may exceed the
size of the buffer and in such case the value is stored with truncation.
This truncations cannot affect the result of the calculation of the range
selectivity as the calculation employes only the beginning of the value
string. However it can trigger generation of an unexpected error on this
truncation if an update statement is processed.
This patch prohibits truncation messages when selectivity of a range
condition is calculated for a non-indexed column.

Approved by Oleksandr Byelkin <sanja@mariadb.com>
This commit is contained in:
Igor Babaev
2023-04-11 21:21:45 -07:00
parent 7bcfa00a6a
commit ef4d09948d
3 changed files with 55 additions and 0 deletions
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29
mysql-test/main/update.result
View File

@ -734,3 +734,32 @@ UPDATE t1,t2 SET t1.i1 = -39 WHERE t2.d1 <> t1.i1 AND t2.d1 = t1.d2;
ERROR 22007: Incorrect datetime value: '19' for column `test`.`t1`.`i1` at row 1
DROP TABLE t1,t2;
# End of MariaDB 10.2 tests
#
# MDEV-20773: UPDATE with LIKE predicate over non-indexed column
# of VARCHAR type
#
create table t1 (a1 varchar(30), a2 varchar(30) collate utf8_bin);
insert into t1 values
('aa','zzz'), ('b','xxaa'), ('ccc','yyy'), ('ddd','xxb');
analyze table t1 persistent for all;
Table Op Msg_type Msg_text
test.t1 analyze status Engine-independent statistics collected
test.t1 analyze status OK
explain extended
update t1 set a1 = 'u'
where a2 like 'xx%' and exists(select 1 from t1 where t1.a1 < 'c');
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t1 ALL NULL NULL NULL NULL 4 49.22 Using where
2 SUBQUERY t1 ALL NULL NULL NULL NULL 4 50.00 Using where
Warnings:
Note 1003 /* select#1 */ update `test`.`t1` set `test`.`t1`.`a1` = 'u' where `test`.`t1`.`a2` like 'xx%'
update t1 set a1 = 'u'
where a2 like 'xx%' and exists(select 1 from t1 where t1.a1 < 'c');
select * from t1;
a1 a2
aa zzz
u xxaa
ccc yyy
u xxb
drop table t1;
# End of MariaDB 10.4 tests

23
mysql-test/main/update.test
View File

@ -676,3 +676,26 @@ UPDATE t1,t2 SET t1.i1 = -39 WHERE t2.d1 <> t1.i1 AND t2.d1 = t1.d2;
DROP TABLE t1,t2;
--echo # End of MariaDB 10.2 tests
--echo #
--echo # MDEV-20773: UPDATE with LIKE predicate over non-indexed column
--echo # of VARCHAR type
--echo #
create table t1 (a1 varchar(30), a2 varchar(30) collate utf8_bin);
insert into t1 values
('aa','zzz'), ('b','xxaa'), ('ccc','yyy'), ('ddd','xxb');
analyze table t1 persistent for all;
explain extended
update t1 set a1 = 'u'
where a2 like 'xx%' and exists(select 1 from t1 where t1.a1 < 'c');
update t1 set a1 = 'u'
where a2 like 'xx%' and exists(select 1 from t1 where t1.a1 < 'c');
select * from t1;
drop table t1;
--echo # End of MariaDB 10.4 tests

3
sql/opt_range.cc
View File

@ -3518,7 +3518,10 @@ bool calculate_cond_selectivity_for_table(THD *thd, TABLE *table, Item **cond)
}
else
{
enum_check_fields save_count_cuted_fields= thd->count_cuted_fields;
thd->count_cuted_fields= CHECK_FIELD_IGNORE;
rows= records_in_column_ranges(&param, idx, key);
thd->count_cuted_fields= save_count_cuted_fields;
if (rows != DBL_MAX)
{
key->field->cond_selectivity= rows/table_records;