CREATE TRIGGER (Transact- SQL). A trigger is a special kind of stored procedure that automatically executes when an event occurs in the database server. 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. For more information, see DML Triggers. DDL triggers execute in response to a variety of data definition language (DDL) events. Comparison of Triggers in MS SQL. In MS SQL the trigger. MS-SQL Server/TSQL Trigger: Update a field only when a specific value is set, otherwise set a different condition. 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. SQL Server allows for creating multiple triggers for any specific statement. For more information on how to mitigate this threat, see Manage Trigger Security. CLR integration does not apply to Azure SQL Database.
DML triggers are scoped to the schema of the table or view on which they are created. Specifying the fully qualified name of the table or view is optional. A view can be referenced only by an INSTEAD OF trigger. DML triggers cannot be defined on local or global temporary tables. DATABASEApplies the scope of a DDL trigger to the current database. If specified, the trigger fires whenever event. If specified, the trigger fires whenever event. Using WITH ENCRYPTION prevents the trigger from being published as part of SQL Server replication. WITH ENCRYPTION cannot be specified for CLR triggers. EXECUTE ASSpecifies the security context under which the trigger is executed. Enables you to control which user account the instance of SQL Server uses to validate permissions on any database objects that are referenced by the trigger. This option is required for triggers on memory- optimized tables. For more information, see. EXECUTE AS Clause (Transact- SQL). NATIVE. All referential cascade actions and constraint checks also must succeed before this trigger fires. AFTER is the default when FOR is the only keyword specified. AFTER triggers cannot be defined on views. INSTEAD OFSpecifies that the DML trigger is executed instead of the triggering SQL statement, therefore, overriding the actions of the triggering statements. INSTEAD OF cannot be specified for DDL or logon triggers. At most, one INSTEAD OF trigger per INSERT, UPDATE, or DELETE statement can be defined on a table or view. However, you can define views on views where each view has its own INSTEAD OF trigger. INSTEAD OF triggers are not allowed on updatable views that use WITH CHECK OPTION. SQL Server raises an error when an INSTEAD OF trigger is added to an updatable view WITH CHECK OPTION specified. The user must remove that option by using ALTER VIEW before defining the INSTEAD OF trigger. At least one option must be specified. Any combination of these options in any order is allowed in the trigger definition. For INSTEAD OF triggers, the DELETE option is not allowed on tables that have a referential relationship specifying a cascade action ON DELETE. Similarly, the UPDATE option is not allowed on tables that have a referential relationship specifying a cascade action ON UPDATE. WITH APPENDApplies to: SQL Server 2. SQL Server 2. 00. R2. Specifies that an additional trigger of an existing type should be added. WITH APPEND cannot be used with INSTEAD OF triggers or if AFTER trigger is explicitly stated. WITH APPEND can be used only when FOR is specified, without INSTEAD OF or AFTER, for backward compatibility reasons. WITH APPEND cannot be specified if EXTERNAL NAME is specified (that is, if the trigger is a CLR trigger). Valid events for DDL triggers are listed in DDL Events. The DDL trigger fires after execution of any Transact- SQL language event that belongs to event. Valid event groups for DDL triggers are listed in DDL Event Groups. After the CREATE TRIGGER has finished running, event. Trigger conditions specify additional criteria that determine whether the tried DML, DDL, or logon events cause the trigger actions to be performed. The trigger actions specified in the Transact- SQL statements go into effect when the operation is tried. Triggers can include any number and kind of Transact- SQL statements, with exceptions. For more information, see Remarks. A trigger is designed to check or change data based on a data modification or definition statement; it should not return data to the user. The Transact- SQL statements in a trigger frequently include control- of- flow language. DML triggers use the deleted and inserted logical (conceptual) tables. They are structurally similar to the table on which the trigger is defined, that is, the table on which the user action is tried. The deleted and inserted tables hold the old values or new values of the rows that may be changed by the user action. For example, to retrieve all values in the deleted table, use: For more information, see Use the inserted and deleted Tables. DDL and logon triggers capture information about the triggering event by using the EVENTDATA (Transact- SQL) function. For more information, see Use the EVENTDATA Function. SQL Server allows for the update of text, ntext, or image columns through the INSTEAD OF trigger on tables or views. Avoid using these data types in new development work, and plan to modify applications that currently use them. Use nvarchar(max), varchar(max), and varbinary(max) instead. Both AFTER and INSTEAD OF triggers support varchar(MAX), nvarchar(MAX), and varbinary(MAX) data in the inserted and deleted tables. For triggers on memory- optimized tables, the only sql. The T- SQL allowed inside the ATOMIC block is limited by the T- SQL allowed inside native procs.< method. The method must take no arguments and return void. If the class has a namespace- qualified name that uses '.' to separate namespace parts, the class name must be delimited by using . The class cannot be a nested class. You can create, modify, and drop database objects that reference managed code modules, but these references will not execute in an instance of SQL Server unless the clr enabled Option is enabled by using sp. SQL Server provides declarative referential integrity (DRI) through the ALTER TABLE and CREATE TABLE statements. However, DRI does not provide cross- database referential integrity. Referential integrity refers to the rules about the relationships between the primary and foreign keys of tables. To enforce referential integrity, use the PRIMARY KEY and FOREIGN KEY constraints in ALTER TABLE and CREATE TABLE. If constraints exist on the trigger table, they are checked after the INSTEAD OF trigger execution and before the AFTER trigger execution. If the constraints are violated, the INSTEAD OF trigger actions are rolled back and the AFTER trigger is not fired. The first and last AFTER triggers to be executed on a table can be specified by using sp. Only one first and one last AFTER trigger for each INSERT, UPDATE, and DELETE operation can be specified on a table. If there are other AFTER triggers on the same table, they are randomly executed. If an ALTER TRIGGER statement changes a first or last trigger, the first or last attribute set on the modified trigger is dropped, and the order value must be reset by using sp. This successful execution includes all referential cascade actions and constraint checks associated with the object updated or deleted. An AFTER trigger will not recursively fire an INSTEAD OF trigger on the same table. If an INSTEAD OF trigger defined on a table executes a statement against the table that would ordinarily fire the INSTEAD OF trigger again, the trigger is not called recursively. Instead, the statement is processed as if the table had no INSTEAD OF trigger and starts the chain of constraint operations and AFTER trigger executions. For example, if a trigger is defined as an INSTEAD OF INSERT trigger for a table, and the trigger executes an INSERT statement on the same table, the INSERT statement executed by the INSTEAD OF trigger does not call the trigger again. The INSERT executed by the trigger starts the process of performing constraint actions and firing any AFTER INSERT triggers defined for the table. If an INSTEAD OF trigger defined on a view executes a statement against the view that would ordinarily fire the INSTEAD OF trigger again, it is not called recursively. Instead, the statement is resolved as modifications against the base tables underlying the view. In this case, the view definition must meet all the restrictions for an updatable view. For a definition of updatable views, see Modify Data Through a View. For example, if a trigger is defined as an INSTEAD OF UPDATE trigger for a view, and the trigger executes an UPDATE statement referencing the same view, the UPDATE statement executed by the INSTEAD OF trigger does not call the trigger again. The UPDATE executed by the trigger is processed against the view as if the view did not have an INSTEAD OF trigger. The columns changed by the UPDATE must be resolved to a single base table. Each modification to an underlying base table starts the chain of applying constraints and firing AFTER triggers defined for the table. Testing for UPDATE or INSERT Actions to Specific Columns. You can design a Transact- SQL trigger to perform certain actions based on UPDATE or INSERT modifications to specific columns. Use UPDATE() or COLUMNS. UPDATE() tests for UPDATE or INSERT tries on one column. The SET option selected remains in effect during the execution of the trigger and then reverts to its former setting. When a trigger fires, results are returned to the calling application, just like with stored procedures.
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