A trigger is a named database object that is associated with a table, and that activates when a particular event occurs for the table.
Some uses for triggers are to perform checks of values to be inserted into a table or to perform calculations on values involved in an update.
A trigger is defined to activate when a statement inserts, updates, or deletes rows in the associated table.
A trigger can be set to activate either before or after the trigger event. For example, you can have a trigger activate before each row that is inserted into a table or after each row that is updated.
