Bug #18807 Undeclared variables are set to empty string, not NULL.

• Submitted: 5 Apr 2006 14:19
• Modified: 14 Apr 2006 8:51
• Reporter: Tobias Asplund
• Status: Duplicate
• Category: MySQL Server
• Severity: S3 (Non-critical)
• Version: 5.0.21-BK, 5.0.19
• OS: Linux (Linux)
• CPU Architecture: Any

[5 Apr 2006 14:19] Tobias Asplund

Description:
If you refer to a variable that has not been initialized, it has a value of NULL and a type of string. (From the manual)

In 5.1 (and < 5.0 versions)
eeyore> SELECT @akdfad;
+---------+
| @akdfad |
+---------+
| NULL    |
+---------+
1 row in set (0.00 sec)

On 5.0:
mysql> SELECT @blah;
+-------+
| @blah |
+-------+
|       |
+-------+
1 row in set (0.10 sec)

How to repeat:
SELECT @asdlkfjalskdjflaksdjflakjdlkfasd;

[5 Apr 2006 14:35] Tobias Asplund

mysql> SELECT IFNULL(@asdfasdfasdfdad, 'no value');
+--------------------------------------+
| IFNULL(@asdfasdfasdfdad, 'no value') |
+--------------------------------------+
| no value                             |
+--------------------------------------+
1 row in set (0.00 sec)

mysql> SELECT @asdfasdfasdfdad;
+------------------+
| @asdfasdfasdfdad |
+------------------+
|                  |
+------------------+
1 row in set (0.00 sec)

Seems like it is NULL, but doesn't display like it would be.......

[5 Apr 2006 14:42] Valeriy Kravchuk

Verified just as described on Linux with 5.0.21-BK (ChangeSet@1.2135, 2006-04-04 15:40:42+05:00).

[11 Apr 2006 12:02] Tobias Asplund

mysql> SELECT CONCAT(NULL);
+--------------+
| CONCAT(NULL) |
+--------------+
|              |
+--------------+
1 row in set (0.00 sec)

Seems to suffer from the same problem.

[12 Apr 2006 13:11] Tobias Asplund

Most likely a duplicate of #18813 - since it displays the same behaviour.

[14 Apr 2006 8:51] Valeriy Kravchuk

Duplicate of bug #18813 (that is marked as a duplicate of another one, not sure why...). Maybe, because it fixed with the same bug fix.