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AFTER triggers are defined only for tables, and multiple AFTER triggers can be defined for the same action. If you have multiple triggers created for the same action, you can specify the first and last triggers to fire by using the sp_settriggerorder system stored procedure. However, any other triggers for the same action are executed in random order.

A trigger defined with the INSTEAD OF clause causes the trigger code to be executed as a replacement for INSERT, UPDATE, or DELETE. You can define a single INSTEAD OF trigger for a given action. Although INSTEAD OF triggers can be created against both tables and views, INSTEAD OF triggers are almost always created against views. Regardless of the number of rows that are affected, a trigger fires only once for an action. The NOT FOR REPLICATION option controls the behavior of the trigger when the replication engine is applying changes. By default, any INSERT, UPDATE, or DELETE executed on a subscriber by the replication engine causes the corresponding trigger to fire. If you do not want the triggers on the subscriber to fire when the replication engine is applying changes, you can specify the NOT FOR REPLICATION option. If a change is being made by any process other than the replication engine, the trigger still fires. When a trigger is executed, two special tables named inserted and deleted are available. These are the same inserted and deleted tables that were explained in 2, Modifying Data The INSERT, UPDATE, DELETE, and MERGE Statements.

DDL triggers can execute either when a DDL statement is executed or when the user logs on to the SQL Server instance. The general syntax for creating a DDL trigger is as follows:

CREATE TRIGGER trigger_name ON { ALL SERVER | DATABASE } [ WITH <ddl_trigger_option> [ ,...n ] ] { FOR | AFTER } { event_type | event_group } [ ,...n ] AS { sql_statement [ ; ] [ ,...n ] | EXTERNAL NAME < method specifier > [ ; ] }

<ddl_trigger_option> ::= [ ENCRYPTION ] [ EXECUTE AS Clause ]

DDL triggers can be scoped at either the database or instance level. To scope a DDL trigger at the instance level, you use the ON ALL SERVER option. To scope a DDL trigger at the database level, you use the ON DATABASE option. The following is an example of a DDL trigger:

CREATE TRIGGER tddl_tabledropalterprevent ON DATABASE FOR DROP_TABLE, ALTER_TABLE AS PRINT 'You are attempting to drop or alter tables in production!' ROLLBACK;

Programming Microsoft SQL Server with T-SQL User-Defined Stored Procedures, Functions, Triggers, and Views

Almost all DDL commands run within the context of a transaction. Because a DDL trigger also runs within the same transaction context, any DDL statement running in the context of a transaction can be rolled back. ALTER DATABASE is one of the commands that does not execute in the context of a transaction because the command affects objects outside SQL Server that do not obey transactional semantics. Therefore, an ALTER DATABASE command cannot be rolled back.

The value for the event type is derived from the DDL statement being executed. Table 5-3 shows several examples.

You can fire a DDL trigger when you grant, revoke, or deny permissions at either a server or a database level. To execute a DDL trigger for a database-level permission statement, use the GRANT_DATABASE, REVOKE_DATABASE, or DENY_DATABASE event types. To execute a DDL trigger for instance-level permissions, use the GRANT_SERVER, REVOKE_SERVER, and DENY_SERVER event types.

Event types roll up within a command hierarchy called event groups. For example, the CREATE_TABLE, ALTER_TABLE, and DROP_TABLE event types are contained within the DDL_TABLE_EVENTS event group. Event types and event groups allow you to create flexible and compact DDL triggers.