Syntax:
SYSDATE()

Returns the current date and time as a value in 'YYYY-MM-DD HH:MM:SS'
or YYYYMMDDHHMMSS format, depending on whether the function is used in
a string or numeric context.

As of MySQL 5.0.13, SYSDATE() returns the time at which it executes.
This differs from the behavior for NOW(), which returns a constant time
that indicates the time at which the statement began to execute.
(Within a stored routine or trigger, NOW() returns the time at which
the routine or triggering statement began to execute.)

mysql> SELECT NOW(), SLEEP(2), NOW();
+---------------------+----------+---------------------+
| NOW()               | SLEEP(2) | NOW()               |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:36 |        0 | 2006-04-12 13:47:36 |
+---------------------+----------+---------------------+

mysql> SELECT SYSDATE(), SLEEP(2), SYSDATE();
+---------------------+----------+---------------------+
| SYSDATE()           | SLEEP(2) | SYSDATE()           |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:44 |        0 | 2006-04-12 13:47:46 |
+---------------------+----------+---------------------+

In addition, the SET TIMESTAMP statement affects the value returned by
NOW() but not by SYSDATE(). This means that timestamp settings in the
binary log have no effect on invocations of SYSDATE().

Because SYSDATE() can return different values even within the same
statement, and is not affected by SET TIMESTAMP, it is
non-deterministic and therefore unsafe for replication. If that is a
problem, you can start the server with the --sysdate-is-now option to
cause SYSDATE() to be an alias for NOW().

URL: http://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html

