From Microsoft site: A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server. DML triggers execute when a user tries to modify data through a data manipulation language (DML) event. DML events are INSERT, UPDATE, or DELETE statements on a table or view. These triggers fire when any valid event is fired, regardless of whether or not any table rows are affected. Here is the full text: http://msdn.microsoft.com/en-us/library/ms189799.aspx
Shanmugappriya, You've posted your question in PHP section, so most likely you are using MySQL. If yes, then it should be useful for you to read the following information: http://dev.mysql.com/doc/refman/5.0/en/triggers.html P.S. It would be better to move this thread to Forum -> Design & Development -> Databases -> MySQL(?) section.
Shanmugappriya, a MySQL trigger is an command you set that triggers (starts) AFTER/BEFORE update,insert (ON UPDATE/INSERT) of any row. I recommend you these schemas http://docs.oracle.com/cd/B19306_01/server.102/b14200/statements_7004.htm hope this is helpfull.