Operating systems such as UNIX/Windows provide a facility called a cron program, which is used to execute certain tasks at specified times and/or repeated at regular intervals at the operating system level. This facility is very useful to run commands on a regularly scheduled basis, to perform periodic operations, to run programs at night for fear of slowing down other users if it were run during the day, and so forth. The Cron is executed at the operating system level.
You need a similar way of scheduling jobs in the database. This article explains job scheduling in the database with an example in detail.
The article continues at http://www.developer.com/db/article.php/3713896