Bug #69109 MySQL 5.0.77 timediff bug
Submitted: 30 Apr 2013 20:05 Modified: 6 May 2013 14:19
Reporter: Doug Ehlenberger Email Updates:
Status: Can't repeat Impact on me:
None 
Category:MySQL Server: General Severity:S2 (Serious)
Version:5.0.77 OS:Linux
Assigned to: CPU Architecture:Any
Tags: timediff

[30 Apr 2013 20:05] Doug Ehlenberger 
Description:
I noticed a possible bug with the timediff function in version 5.0.77. The details of this are presented in the How to repeat section. A series of queries and the output produced by them are shown. Is timediff() actually returning a time value? It seems I have to explicitly cast it to a time value to make the comparison work? See below.

How to repeat:
select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
output: 06:00:00, 02:50:00 (correct 6 hours and 2 hours 50 minutes) 

select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
output: 1 (incorrect 6 hours is not less than 2 hours 50 minutes?)

select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
output: 1 (incorrect 6 hours is not less than 2 hours 50 minutes?)

select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
output: 1 (incorrect 6 hours is not less than 2 hours 50 minutes?)

select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
output: 0 (correct)

select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
output: 0 (correct)

select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
output: 0 (correct)

select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
output: 0 (correct)

select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
output: 0 (correct)

Suggested fix:
Make sure timediff() is actually returning a time value as indicated in the documentation.
[6 May 2013 14:19] MySQL Verification Team 
Thanks for your report, I can't reproduce your problem with the latest GA versions( 5.5.x, 5.6.x, 5.1.x and 5.0.x)

We do not fix bugs that are not repeatable with current versions.
[6 May 2013 14:22] MySQL Verification Team 
### 5.6.11  - works as expected

[root@ushastry mysql-5.6.11-release]# bin/mysql -u root -p --port=3306 --protocol=TCP test
Enter password: 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.11-debug-log Source distribution

Copyright (c) 2000, 2013, 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> 
mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
+----------------------------------------------------------+---------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) | time( 25000 ) |
+----------------------------------------------------------+---------------+
| 06:00:00                                                 | 02:50:00      |
+----------------------------------------------------------+---------------+
1 row in set (0.01 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
+---------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 ) |
+---------------------------------------------------------------------------+
|                                                                         0 |
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
+--------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' ) |
+--------------------------------------------------------------------------------+
|                                                                              0 |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
+----------------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time ) |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
+------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00' |
+------------------------------------------------------------------------+
|                                                                      0 |
+------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
+-------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 ) |
+-------------------------------------------------------------------------------------------+
|                                                                                         0 |
+-------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
+------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' ) |
+------------------------------------------------------------------------------------------------+
|                                                                                              0 |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
+--------------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time ) |
+--------------------------------------------------------------------------------------------------------+
|                                                                                                      0 |
+--------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
+----------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00' |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
[6 May 2013 14:22] MySQL Verification Team 
### 5.5.31  - works as expected

root@ushastry mysql-5.5.31]# 130501 10:58:38 mysqld_safe Logging to '/tmp/5531_/ushastry.err'.
130501 10:58:39 mysqld_safe Starting mysqld daemon with databases from /tmp/5531_

[root@ushastry mysql-5.5.31]# bin/mysql -u root -p --port=3306 --protocol=TCP test
Enter password: 
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.5.31-debug-log Source distribution

Copyright (c) 2000, 2013, 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> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
+----------------------------------------------------------+---------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) | time( 25000 ) |
+----------------------------------------------------------+---------------+
| 06:00:00                                                 | 02:50:00      |
+----------------------------------------------------------+---------------+
1 row in set (0.03 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
+---------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 ) |
+---------------------------------------------------------------------------+
|                                                                         0 |
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
+--------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' ) |
+--------------------------------------------------------------------------------+
|                                                                              0 |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
+----------------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time ) |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
+------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00' |
+------------------------------------------------------------------------+
|                                                                      0 |
+------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
+-------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 ) |
+-------------------------------------------------------------------------------------------+
|                                                                                         0 |
+-------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
+------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' ) |
+------------------------------------------------------------------------------------------------+
|                                                                                              0 |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
+--------------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time ) |
+--------------------------------------------------------------------------------------------------------+
|                                                                                                      0 |
+--------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
+----------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00' |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
[6 May 2013 14:23] MySQL Verification Team 
### 5.1.68 - works as expected

[root@cluster-repo mysql-5.1.68]# bin/mysql -u root -p --port=5168 --protocol=TCP
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.1.68 MySQL Community Server (GPL)

Copyright (c) 2000, 2013, 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>
mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
+----------------------------------------------------------+---------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) | time( 25000 ) |
+----------------------------------------------------------+---------------+
| 06:00:00                                                 | 02:50:00      |
+----------------------------------------------------------+---------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
+---------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 ) |
+---------------------------------------------------------------------------+
|                                                                         0 |
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
+--------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' ) |
+--------------------------------------------------------------------------------+
|                                                                              0 |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
+----------------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time ) |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
+------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00' |
+------------------------------------------------------------------------+
|                                                                      0 |
+------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
+-------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 ) |
+-------------------------------------------------------------------------------------------+
|                                                                                         0 |
+-------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
+------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' ) |
+------------------------------------------------------------------------------------------------+
|                                                                                              0 |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
+--------------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time ) |
+--------------------------------------------------------------------------------------------------------+
|                                                                                                      0 |
+--------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
+----------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00' |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql>
[6 May 2013 14:23] MySQL Verification Team 
### 5.0.96  - works as expected

[root@cluster-repo mysql-5.0.96]# bin/mysql -u root -p --port=5096 --protocol=TCP
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.96 MySQL Community Server (GPL)

Copyright (c) 2000, 2011, 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>
mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
+----------------------------------------------------------+---------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) | time( 25000 ) |
+----------------------------------------------------------+---------------+
| 06:00:00                                                 | 02:50:00      |
+----------------------------------------------------------+---------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
+---------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 ) |
+---------------------------------------------------------------------------+
|                                                                         0 |
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
+--------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' ) |
+--------------------------------------------------------------------------------+
|                                                                              0 |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
+----------------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time ) |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
+------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00' |
+------------------------------------------------------------------------+
|                                                                      0 |
+------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
+-------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 ) |
+-------------------------------------------------------------------------------------------+
|                                                                                         0 |
+-------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
+------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' ) |
+------------------------------------------------------------------------------------------------+
|                                                                                              0 |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
+--------------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time ) |
+--------------------------------------------------------------------------------------------------------+
|                                                                                                      0 |
+--------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
+----------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00' |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
[6 May 2013 14:24] MySQL Verification Team 
#### 5.0.77  - affected

[root@cluster-repo mysql-5.0.77]# bin/mysql -u root -p --port=5077 --protocol=TCP
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.0.77 MySQL Community Server (GPL)

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql>
mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ), time( 25000 );
+----------------------------------------------------------+---------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) | time( 25000 ) |
+----------------------------------------------------------+---------------+
| 06:00:00                                                 | 02:50:00      |
+----------------------------------------------------------+---------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 );
+---------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( 25000 ) |
+---------------------------------------------------------------------------+
|                                                                         1 |
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' );
+--------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= time( '02:50:00' ) |
+--------------------------------------------------------------------------------+
|                                                                              1 |
+--------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time );
+----------------------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= cast( '02:50:00' as time ) |
+----------------------------------------------------------------------------------------+
|                                                                                      1 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00';
+------------------------------------------------------------------------+
| timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) <= '02:50:00' |
+------------------------------------------------------------------------+
|                                                                      0 |
+------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 );
+-------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( 25000 ) |
+-------------------------------------------------------------------------------------------+
|                                                                                         0 |
+-------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' );
+------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= time( '02:50:00' ) |
+------------------------------------------------------------------------------------------------+
|                                                                                              0 |
+------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time );
+--------------------------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= cast( '02:50:00' as time ) |
+--------------------------------------------------------------------------------------------------------+
|                                                                                                      0 |
+--------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

mysql> select cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00';
+----------------------------------------------------------------------------------------+
| cast( timediff( '2013-04-28 20:10:00', '2013-04-28 14:10:00' ) as time ) <= '02:50:00' |
+----------------------------------------------------------------------------------------+
|                                                                                      0 |
+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)