Why triggers in sql

If we want to query the table in the same trigger, then we should use the AFTER keyword, because triggers can query the table or change it again only after the initial changes are applied and the table is back. This brings us to the end of this blog — Triggers in SQL. I hope you understood the concepts of Triggers.

See you all in another blog. Save my name, email, and website in this browser for the next time I comment. Home Blog Whitepapers Glossary. Sign in. When we insert data into a view by the following query then it inserts values in both tables :. I hope this article has helped you in understanding this topic. Please share it.

If you know more about this, your feedback and constructive contributions are welcome. Continue learning more, Trigger in SQL. View All. Triggers in SQL Server. Deepak Middha Updated date Jul 01, So, write triggers to lessen their duration whenever possible.

One way to achieve shorter duration is to release a trigger when a DML statement changes zero rows. The following T-SQL code snippet shows how to release the trigger for a command that doesn't change any rows.

This code should be present at the beginning of each DML trigger:. DDL triggers, like standard triggers, launch stored procedures in response to an event.

Instead, they primarily run in response to data definition language DDL statements. Test your DDL triggers to determine their responses to system stored procedure execution.

DDL triggers don't fire in response to events that affect local or global temporary tables and stored procedures.

Use the catalog views instead. This folder is located under the Server Objects folder. This folder is located under the Programmability folder of the corresponding database. This event happens when a user session is established with an instance of SQL Server.

Logon triggers fire after the authentication phase of logging in finishes, but before the user session is established. So, all messages originating inside the trigger that would typically reach the user, such as error messages and messages from the PRINT statement, are diverted to the SQL Server error log. For more information, see Logon Triggers. Distributed transactions aren't supported in a logon trigger. Error returns when a logon trigger that contains a distributed transaction fire.

A logon trigger can effectively prevent successful connections to the Database Engine for all users, including members of the sysadmin fixed server role. When a logon trigger is preventing connections, members of the sysadmin fixed server role can connect by using the dedicated administrator connection, or by starting the Database Engine in minimal configuration mode -f.

The ability to return results from triggers will be removed in a future version of SQL Server. Triggers that return result sets may cause unexpected behavior in applications that aren't designed to work with them. Avoid returning result sets from triggers in new development work, and plan to modify applications that currently do.

To prevent triggers from returning result sets, set the disallow results from triggers option to 1. Logon triggers always disallow the return of results sets and this behavior isn't configurable. If a logon trigger generates a result set, the trigger fails to launch and the login attempt that fired the trigger is denied. With indirect recursion, an application updates table T1. This fires trigger TR1, updating table T2. Trigger T2 then fires and updates table T1.

In direct recursion, the application updates table T1. This fires trigger TR1, updating table T1. Because table T1 was updated, trigger TR1 fires again, and so on. The following example uses both indirect and direct trigger recursion Assume that two update triggers, TR1 and TR2, are defined on table T1. Trigger TR1 updates table T1 recursively. The inserted and deleted tables for a specific trigger contain rows that correspond only to the UPDATE statement that invoked the trigger. There's no defined order in which multiple triggers defined for a specific event are run.

Each trigger should be self-contained. You can nest triggers to a maximum of 32 levels. If a trigger changes a table on which there's another trigger, the second trigger activates and can then call a third trigger, and so on.

If any trigger in the chain sets off an infinite loop, the nesting level is exceeded and the trigger is canceled. When a Transact-SQL trigger launches managed code by referencing a CLR routine, type, or aggregate, this reference counts as one level against the level nesting limit. Methods invoked from within managed code don't count against this limit. The default configuration supports nested triggers. Review your applications for nested triggers to determine if the applications follow your business rules when the nested triggers server configuration option is set to 0.