Trigger in SQL Server is a special form of stored procedure that we could use to modify data that executes when a certain (DML or DDL) event occurs. A DML event includes INSERT, UPDATE and DELETE while DDL event includes CREATE, ALTER, and DROP.
Triggers are always part of the transition we are working on. This could be both advantageous since we could always roll them back and they could also be disadvantageous because it extends the transaction we are working on.
DML Triggers make use of two logical (memory-resident) tables INSERTED and DELETED. For insert operation we could us INSERTED table to get the new image of the affected rows. For delete operation we could use DELETED table to get the old image of the affected rows. Since update statement is a combination of deleting the old one and inserting the new value we use both DELETED and INSERTED to get the values we for our operations respectively.
There are two types of DML triggers INSTEAD OF triggers and AFTER triggers.
Follow the link above to explore and find examples on triggers.
Read More
http://technet.microsoft.com/en-us/library/ms189799.aspx
Full Service Business Data Solutions
