Use triggers that many people do not understand, with their use, according to the functional separation has many different categories, Changzhou trigger basically divided into the following three categories. DML triggers: When data changes in the database tables, including insert, update, delete any operation, if we write the corresponding table DML triggers, then the trigger automatically. The main role of DML triggers that enforce business rules, and extended Sql Server constraints, defaults and so on. Because we know only constraint constraint data in the same table, and trigger Sql can execute arbitrary commands. DDL Triggers: it is Sql Server2005 new trigger, mainly for review and regulate the operation of the structure of the database tables, triggers, views, etc. For example, in modified form, modify the column, the new tables, new column and so on. It is executed when the database structure changes, we mainly use it to record the revision process of the database, as well as restrictions on the programmer to modify the database, such as certain specified table and so can not be deleted. Login Triggers: logon trigger for stored procedures and stimulate a response LOGIN events. This event is raised when a user session is established with the SQL Server instance. Login trigger after login authentication phase is completed and the user session before the actual establishment of excitation. Therefore, all messages (such as error messages and messages from the PRINT statement) from within a trigger, and usually will reach the user is transferred to the SQL Server error log. If the authentication fails, will not stimulate the login trigger. The basic function of the above is roughly Changzhou trigger. Changzhou lamp factory, Changzhou ballast, Changzhou trigger www.czleneng.com