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Keep in mind that the order of execution is lost when the trigger is altered you must reset it again using sp_SetTriggerOrder.
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Renaming Triggers Triggers are often renamed using Transact-SQL statements designed for the creation and modification of triggers, such as Alter Trigger. As with all other database objects, a trigger can be forced to change its name using the following system stored procedure:
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Exec sp_rename 'Orders_Trigger1', 'trOrders_IU'
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The first parameter is the current name of the database object, and the second parameter is the new name of the object. Disabling Triggers dropping them: It is possible to temporarily disable and enable triggers without
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Alter Table [Order] Disable Trigger trOrders_IU
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After the execution of this statement, the specified trigger will not fire, but it will still be associated with the table. This technique is often used to load large amounts of data into a table without initiating the business logic encapsulated in a trigger.
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Since triggers are relatively complex database objects, it is easy to create design, performance, or maintainability problems inside your database. Therefore, I will spend some time pointing out a proper way to use them.
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Go out ASAP
Triggers take time to execute. If your server is very busy and/or other users are locking resources in the database, execution might take much more time than expected. On the other hand, locks that you (or rather SQL Server) have placed in the database while the trigger is executing will not be released until the trigger is finished. Thus, your trigger may increase competition for resources and affect other users and their sessions. For these reasons, you should always try to exit a trigger as soon as possible. For example, you could start (almost) every trigger with the following test:
If @@rowcount = 0 Return
It will abort further execution of the trigger if no records were changed. Keep in mind that this If clause must occur at the very beginning of the trigger. If you put it after any other statement, @@rowcount will return the number of records affected by that statement. For example, if you put a simple Print statement at the beginning of the trigger and then this test, the remainder of the trigger will not be executed:
Alter Trigger trOrderStatus_U On dbo.[Order] After Update -- For Update As Print 'Start of trOrderStatus_U' If @@Rowcount = 0 -- This is always true -- and the rest will NEVER be executed. Return If Update (OrderStatusId) Begin Insert into ActivityLog( Activity, LogDate, UserName,
C h a p t e r 8 : S p e c i a l Ty p e s o f P r o c e d u r e s
Select
Note) 'Order.OrderStatusId', GetDate(), USER_NAME(), 'Value changed from ' + Cast( d.OrderStatusId as varchar) + ' to ' + Cast( i.OrderStatusId as varchar)
From deleted d inner join inserted i On d.OrderId = i.OrderId End
Make It Simple
It is true that triggers are suitable for implementing complex business rules, particularly if those business rules are too complex to be handled by simpler database objects such as constraints. However, just because you are using them to handle complex business rules, you do not have to make your code so complex that it is difficult to understand and follow. It is challenging enough to work with triggers: keep them as simple as possible.
Divide and Conquer
In earlier versions of Microsoft SQL Server, only one trigger per modification statement could be associated with a table. This physical restriction led developers to produce poor code. Features that were not related had to be piled up in a single trigger. However, this restriction no longer applies. There is no reason to couple the code for multiple triggers. Each distinct piece of functionality can be implemented in a separate trigger (except in the case of Instead-of triggers).
Do Not Use Select and Print Inside a Trigger
The Print and Select commands are very useful in triggers during the debugging process. However, they can be very dangerous if left in a trigger after it has been introduced into production. These statements generate additional result sets, which might cause the client application to fail if it is not able to handle them or does not expect them.
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