Bug #79924 Func CONVERT and CONVERT(,BINARY) works incorrect w/ multi-byte+multi-rows

• Submitted: 12 Jan 2016 6:38
• Modified: 21 Jan 2016 23:04
• Reporter: Su Dylan
• Status: Closed
• Category: MySQL Server: DML
• Severity: S2 (Serious)
• Version: 5.7.8, 5.5.48, 5.6.28, 5.7.10
• OS: Any
• CPU Architecture: Any

[12 Jan 2016 6:38] Su Dylan

Description:
Output:
=====
mysql> create table t1(c1 int);
Query OK, 0 rows affected (0.00 sec)

mysql> insert into t1 values(1),(2),(3);
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> select convert( substr('大不列颠及北爱尔兰联合王国', 1, 15), BINARY) from t1;
+----------------------------------------------------------------------------+
| convert( substr('大不列颠及北爱尔兰联合王国', 1, 15), BINARY) |
+----------------------------------------------------------------------------+
| 大不列颠及北爱尔兰联合王国                                    |
| 大不列颠及                                                            |
| 大不列颠及                                                            |
+----------------------------------------------------------------------------+
3 rows in set (0.00 sec)

Problem:
=====
The select item is a constant, same result expected for each row.

How to repeat:

set names 'utf8';
drop table if exists t1;
create table t1(c1 int);
insert into t1 values(1),(2),(3);
select convert( substr('大不列颠及北爱尔兰联合王国', 1, 15), BINARY) from t1;

Suggested fix:
'大不列颠及北爱尔兰联合王国' is returned for each row.

[12 Jan 2016 7:29] MySQL Verification Team

Hello Su Dylan,

Thank you for the report and test case.
Observed that 5.5.48/5.6.28/5.7.10 are affected.

Thanks,
Umesh

[21 Jan 2016 23:04] Paul DuBois

Noted in 5.8.0 changelog.

For calls to CONVERT(), literal string arguments could be modified
during execution, producing incorrect results.