Programming in MS SQL Server 2012

TRIGGER



SQL Server Triggers are a special kind of stored procedure that executes automatically when a user attempts the specified UPDATE, INSERT or DELETE data modificatin statement on the specified table or view object based on business rules. Triggers can extend the data integrity checking logic of SQL Server constraints, defaults, and rules. Tables can have multiple DML triggers and only one INSTEAD OF triger.

Types of Triggers

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.

DDL triggers execute in response to a variety of data definition language (DDL) events. These events primarily correspond to Transact-SQL CREATE, ALTER, and DROP statements, and certain system stored procedures that perform DDL-like operations.

Logon triggers fire in response to the LOGON event that is raised when a user sessions is being established. Triggers can be created directly from Transact-SQL statements or from methods of assemblies that are created in the Microsoft .NET Framework common language runtime (CLR) and uploaded to an instance of SQL Server. SQL Server allows for creating multiple triggers for any specific statement.

Types of DML Triggers

AFTER triggers are executed after the action of the INSERT, UPDATE, or DELETE statement is performed. Specifying AFTER is the same as specifying FOR, which is the only option available in earlier versions of Microsoft SQL Server. This AFTER triggers can be specified only on tables.

INSTEAD OF triggers are executed in place of the usual triggering action. INSTEAD OF triggers can also be defined on views with one or more base tables, where they can extend the types of updates a view can support.

CLR Trigger can be either an AFTER or INSTEAD OF trigger. A CLR trigger can also be a DDL trigger. Instead of executing a Transact-SQL stored procedure, a CLR trigger executes one or more methods written in managed code that are members of an assembly created in the .NET Framework and uploaded in SQL Server.

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