[MDEV-8369] Unexpected impossible WHERE for a condition on a ZEROFILL field - Jira

Details

Type: Bug
Status: Closed (View Workflow)
Priority: Major
Resolution: Fixed
Affects Version/s: 5.5(EOL), 10.0(EOL), 10.1(EOL)
Fix Version/s: 10.1.8
Component/s: Optimizer
Labels:
None

Description

This script:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a INT ZEROFILL);

INSERT INTO t1 VALUES (128);

SELECT * FROM t1 WHERE a=128;

SELECT * FROM t1 WHERE hex(a)='80';

correctly returns one row for both SELECT queries.

if I join the two conditions using AND:

SELECT * FROM t1 WHERE a=128 AND hex(a)='80';

it unexpectedly returns Empty set.

EXPLAIN for the above query tells "Impossible WHERE":

MariaDB [test]> EXPLAIN SELECT * FROM t1 WHERE a=128 AND hex(a)='80';

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra            |

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

|    1 | SIMPLE      | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL | Impossible WHERE |

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

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blocks

MDEV-8728 Fix a number of problems in equal field and equal expression propagation

Closed

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Alexander Barkov created issue - 2015-06-24 13:01

Alexander Barkov made changes - 2015-06-24 13:02

Field	Original Value	New Value
Description	This script: {code} DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT ZEROFILL); INSERT INTO t1 VALUES (128); SELECT * FROM t1 WHERE a=128; SELECT * FROM t1 WHERE hex(a)='80'; {code} correctly returns one row for both SELECT queries. if I join the two conditions using AND: {code} SELECT * FROM t1 WHERE a=128 AND hex(a)='80'; {code} EXPLAIN for the above query tells "Impossible WHERE": {noformat} MariaDB [test]> EXPLAIN SELECT * FROM t1 WHERE a=128 AND hex(a)='80';+------+-------------+-------+------+---------------+------+---------+------+------+------------------+ \| id \| select_type \| table \| type \| possible_keys \| key \| key_len \| ref \| rows \| Extra \| +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ \| 1 \| SIMPLE \| NULL \| NULL \| NULL \| NULL \| NULL \| NULL \| NULL \| Impossible WHERE \| +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ {noformat}	This script: {code} DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT ZEROFILL); INSERT INTO t1 VALUES (128); SELECT * FROM t1 WHERE a=128; SELECT * FROM t1 WHERE hex(a)='80'; {code} correctly returns one row for both SELECT queries. if I join the two conditions using AND: {code} SELECT * FROM t1 WHERE a=128 AND hex(a)='80'; {code} it unexpectedly returns Empty set. EXPLAIN for the above query tells "Impossible WHERE": {noformat} MariaDB [test]> EXPLAIN SELECT * FROM t1 WHERE a=128 AND hex(a)='80';+------+-------------+-------+------+---------------+------+---------+------+------+------------------+ \| id \| select_type \| table \| type \| possible_keys \| key \| key_len \| ref \| rows \| Extra \| +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ \| 1 \| SIMPLE \| NULL \| NULL \| NULL \| NULL \| NULL \| NULL \| NULL \| Impossible WHERE \| +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ {noformat}

Alexander Barkov made changes - 2015-06-24 13:03

Description

This script:
{code}
DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a INT ZEROFILL);
INSERT INTO t1 VALUES (128);
SELECT * FROM t1 WHERE a=128;
SELECT * FROM t1 WHERE hex(a)='80';
{code}
correctly returns one row for both SELECT queries.

if I join the two conditions using AND:
{code}
SELECT * FROM t1 WHERE a=128 AND hex(a)='80';
{code}
it unexpectedly returns Empty set.

EXPLAIN for the above query tells "Impossible WHERE":
{noformat}
MariaDB [test]> EXPLAIN SELECT * FROM t1 WHERE a=128 AND hex(a)='80';+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
{noformat}

This script:
{code}
DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a INT ZEROFILL);
INSERT INTO t1 VALUES (128);
SELECT * FROM t1 WHERE a=128;
SELECT * FROM t1 WHERE hex(a)='80';
{code}
correctly returns one row for both SELECT queries.

if I join the two conditions using AND:
{code}
SELECT * FROM t1 WHERE a=128 AND hex(a)='80';
{code}
it unexpectedly returns Empty set.

EXPLAIN for the above query tells "Impossible WHERE":
{noformat}
MariaDB [test]> EXPLAIN SELECT * FROM t1 WHERE a=128 AND hex(a)='80';
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
| 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
{noformat}

Jiri Kavalik added a comment - 2015-06-24 13:21 - edited

explain extended SELECT * FROM t1 WHERE a=128 AND hex(a)='80';

show warnings;

+-------+------+--------------------------------------------------------+

| Level | Code | Message                                                |

+-------+------+--------------------------------------------------------+

| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where 0 |

+-------+------+--------------------------------------------------------+

and without zerofil

explain extended SELECT * FROM t1 WHERE a=128 AND hex(a)='80';

+-------+------+------------------------------------------------------------------------------+

| Level | Code | Message                                                                      |

+-------+------+------------------------------------------------------------------------------+

| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where (`test`.`t1`.`a` = 128) |

+-------+------+------------------------------------------------------------------------------+

Jiri Kavalik added a comment - 2015-06-24 13:21 - edited explain extended SELECT * FROM t1 WHERE a=128 AND hex(a)='80'; show warnings; +-------+------+--------------------------------------------------------+ | Level | Code | Message | +-------+------+--------------------------------------------------------+ | Note | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where 0 | +-------+------+--------------------------------------------------------+ and without zerofil explain extended SELECT * FROM t1 WHERE a=128 AND hex(a)='80'; +-------+------+------------------------------------------------------------------------------+ | Level | Code | Message | +-------+------+------------------------------------------------------------------------------+ | Note | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where (`test`.`t1`.`a` = 128) | +-------+------+------------------------------------------------------------------------------+

Alexander Barkov added a comment - 2015-08-20 13:36 - edited

The problem happens because optimize_cond() when propagating equalities replaces the condition to:

WHERE a=128 AND hex('0000000128')='80'

which later evaluates to FALSE because HEX() returns hex representations of the string rather than hex representation of the original number 128.

convert_zerofill_number_to_string() is the function which actually replaces Item_field to Item_string is .

Alexander Barkov added a comment - 2015-08-20 13:36 - edited The problem happens because optimize_cond() when propagating equalities replaces the condition to: WHERE a=128 AND hex('0000000128')='80' which later evaluates to FALSE because HEX() returns hex representations of the string rather than hex representation of the original number 128. convert_zerofill_number_to_string() is the function which actually replaces Item_field to Item_string is .

Alexander Barkov added a comment - 2015-08-21 09:30

This script demonstrates a similar problem:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a INT(6) ZEROFILL);

INSERT INTO t1 VALUES (1);

SELECT * FROM t1 WHERE a=1;

SELECT * FROM t1 WHERE DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin; SELECT * FROM t1 WHERE a=1 AND DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin;

The first and the second SELECT return one row. The third SELECT returns empty set.
EXPLAIN for the third SELECT:

EXPLAIN SELECT * FROM t1 WHERE a=1 AND DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin;

returns

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra            |

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

|    1 | SIMPLE      | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL | Impossible WHERE |

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

Alexander Barkov added a comment - 2015-08-21 09:30 This script demonstrates a similar problem: DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT(6) ZEROFILL); INSERT INTO t1 VALUES (1); SELECT * FROM t1 WHERE a=1; SELECT * FROM t1 WHERE DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin; SELECT * FROM t1 WHERE a=1 AND DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin; The first and the second SELECT return one row. The third SELECT returns empty set. EXPLAIN for the third SELECT: EXPLAIN SELECT * FROM t1 WHERE a=1 AND DES_ENCRYPT('test',a)=_latin1 0x8104A375CC9BD44E7C COLLATE latin1_bin; returns +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +------+-------------+-------+------+---------------+------+---------+------+------+------------------+ | 1 | SIMPLE | NULL | NULL | NULL | NULL | NULL | NULL | NULL | Impossible WHERE | +------+-------------+-------+------+---------------+------+---------+------+------+------------------+

Alexander Barkov added a comment - 2015-08-21 09:54

A similar example with WEIGHT_STRING:

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a INT(6) ZEROFILL);

INSERT INTO t1 VALUES (1);

SELECT * FROM t1 WHERE a=1;

SELECT * FROM t1 WHERE WEIGHT_STRING(a) IS NULL;

SELECT * FROM t1 WHERE a=1 AND WEIGHT_STRING(a) IS  NULL;

Alexander Barkov added a comment - 2015-08-21 09:54 A similar example with WEIGHT_STRING: DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a INT(6) ZEROFILL); INSERT INTO t1 VALUES (1); SELECT * FROM t1 WHERE a=1; SELECT * FROM t1 WHERE WEIGHT_STRING(a) IS NULL; SELECT * FROM t1 WHERE a=1 AND WEIGHT_STRING(a) IS NULL;

Alexander Barkov added a comment - 2015-08-21 10:02 - edited

A similar example using FORMAT():

DROP TABLE IF EXISTS t1;

CREATE TABLE t1 (a BIGINT(20) ZEROFILL);

INSERT INTO t1 VALUES (18446744073709551615);

SELECT * FROM t1 WHERE a=18446744073709551615;

SELECT * FROM t1 WHERE FORMAT(a,0)='18,446,744,073,709,551,615';

SELECT * FROM t1 WHERE a=18446744073709551615 AND FORMAT(a,0)='18,446,744,073,709,551,615';

Alexander Barkov added a comment - 2015-08-21 10:02 - edited A similar example using FORMAT(): DROP TABLE IF EXISTS t1; CREATE TABLE t1 (a BIGINT(20) ZEROFILL); INSERT INTO t1 VALUES (18446744073709551615); SELECT * FROM t1 WHERE a=18446744073709551615; SELECT * FROM t1 WHERE FORMAT(a,0)='18,446,744,073,709,551,615'; SELECT * FROM t1 WHERE a=18446744073709551615 AND FORMAT(a,0)='18,446,744,073,709,551,615';

Alexander Barkov made changes - 2015-09-02 06:51

Link

This issue blocks ~~MDEV-8728~~ [ ~~MDEV-8728~~ ]

Alexander Barkov made changes - 2015-09-11 13:06

Status

Open [ 1 ]

In Progress [ 3 ]

Alexander Barkov made changes - 2015-09-11 14:46

Component/s		OTHER [ 10125 ]
Fix Version/s		10.1.8 [ 19605 ]
Fix Version/s	10.1 [ 16100 ]
Resolution		Fixed [ 1 ]
Status	In Progress [ 3 ]	Closed [ 6 ]

Sergei Golubchik made changes - 2015-09-14 09:50

Component/s		Optimizer [ 10200 ]
Component/s	OTHER [ 10125 ]

Sergei Golubchik made changes - 2021-12-06 21:41

Workflow

MariaDB v3 [ 70310 ]

MariaDB v4 [ 149297 ]

People

Assignee:: Alexander Barkov

Reporter:: Alexander Barkov

Votes:: 0 Vote for this issue

Watchers:: 3 Start watching this issue

Dates

Created:: 2015-06-24 13:01

Updated:: 2015-09-14 09:50

Resolved:: 2015-09-11 14:46

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