Bug #75668 Use of Distinct, Group_concat, and Group by together produces 1 NULL row result.

• Submitted: 28 Jan 2015 16:21
• Modified: 28 Jan 2015 20:06
• Reporter: Jonathan Moore
• Status: Verified
• Category: MySQL Server: Optimizer
• Severity: S2 (Serious)
• Version: 5.6.22/5.7
• OS: FreeBSD (FreeBSD 8.4)
• CPU Architecture: Any
• Tags: regression

[28 Jan 2015 16:21] Jonathan Moore

Description:
Current Output:
mysql> select distinct trim(group_concat(A)) from TEST_JM group by B;
+-----------------------+
| trim(group_concat(A)) |
+-----------------------+
| NULL                  |
+-----------------------+
1 row in set (0.00 sec)

Expected output:
mysql> SELECT DISTINCT TRIM(GROUP_CONCAT(id)) FROM test GROUP BY id;
+------------------------+
| TRIM(GROUP_CONCAT(id)) |
+------------------------+
| 1                      |
| 2                      |
+------------------------+
2 rows in set (0.00 sec)

The expected output is from a MySQl 5.1.42 server.

How to repeat:
CREATE TABLE IF NOT EXISTS `test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=myisam DEFAULT CHARSET=latin1;

INSERT INTO test values(1), (2);

SELECT DISTINCT TRIM(GROUP_CONCAT(id)) FROM test GROUP BY id

[28 Jan 2015 20:03] MySQL Verification Team

C:\dbs>c:\dbs\5.5\bin\mysql -uroot --port=3550 --prompt="mysql 5.5 > "
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.5.43 Source distribution

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql 5.5 > use test
Database changed
mysql 5.5 > CREATE TABLE IF NOT EXISTS `test` (
    ->   `id` int(11) NOT NULL AUTO_INCREMENT,
    ->   PRIMARY KEY (`id`)
    -> ) ENGINE=myisam DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.03 sec)

mysql 5.5 >
mysql 5.5 > INSERT INTO test values(1), (2);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.5 >
mysql 5.5 > SELECT DISTINCT TRIM(GROUP_CONCAT(id)) FROM test GROUP BY id;
+------------------------+
| TRIM(GROUP_CONCAT(id)) |
+------------------------+
| 1                      |
| 2                      |
+------------------------+
2 rows in set (0.03 sec)

----------------------------------------------------------------------------------

C:\dbs>c:\dbs\5.6\bin\mysql -uroot --port=3560 --debug-info --prompt="mysql 5.6 > "
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.6.24 Source distribution

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql 5.6 > use test
Database changed
mysql 5.6 > CREATE TABLE IF NOT EXISTS `test` (
    ->   `id` int(11) NOT NULL AUTO_INCREMENT,
    ->   PRIMARY KEY (`id`)
    -> ) ENGINE=myisam DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.03 sec)

mysql 5.6 >
mysql 5.6 > INSERT INTO test values(1), (2);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.6 >
mysql 5.6 > SELECT DISTINCT TRIM(GROUP_CONCAT(id)) FROM test GROUP BY id;
+------------------------+
| TRIM(GROUP_CONCAT(id)) |
+------------------------+
| NULL                   |
+------------------------+
1 row in set (0.01 sec)

[28 Jan 2015 20:06] MySQL Verification Team

Thank you for the bug report.

[28 Jan 2015 20:07] MySQL Verification Team

C:\dbs>net start mysqld57
The MySQLD57 service is starting.
The MySQLD57 service was started successfully.

C:\dbs>57

C:\dbs>c:\dbs\5.7\bin\mysql -uroot --port=3570 --prompt="mysql 5.7 > "
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.7.6-m16 Source distribution

Copyright (c) 2000, 2015, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql 5.7 > use test
Database changed
mysql 5.7 > CREATE TABLE IF NOT EXISTS `test` (
    ->   `id` int(11) NOT NULL AUTO_INCREMENT,
    ->   PRIMARY KEY (`id`)
    -> ) ENGINE=myisam DEFAULT CHARSET=latin1;
Query OK, 0 rows affected (0.08 sec)

mysql 5.7 >
mysql 5.7 > INSERT INTO test values(1), (2);
Query OK, 2 rows affected (0.00 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql 5.7 >
mysql 5.7 > SELECT DISTINCT TRIM(GROUP_CONCAT(id)) FROM test GROUP BY id;
+------------------------+
| TRIM(GROUP_CONCAT(id)) |
+------------------------+
| NULL                   |
+------------------------+
1 row in set (0.00 sec)

mysql 5.7 >