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Using "instead of" triggers

From: SQL Server: Triggers, Stored Procedures, and Functions

Video: Using "instead of" triggers

The next type of triggers we will talk about are 'instead of' triggers. These triggers are executed as an alternative to an INSERT, UPDATE, or DELETE statement. These triggers completely block the original statement leaving the data unchanged. However, inside the body of the trigger we can choose to modify data and we usually do. In this example, I'll be of using a trigger to enforce a data integrity rule. The rule states that we cannot ever delete a category. We must just mark that category as inactive.

Using "instead of" triggers

The next type of triggers we will talk about are 'instead of' triggers. These triggers are executed as an alternative to an INSERT, UPDATE, or DELETE statement. These triggers completely block the original statement leaving the data unchanged. However, inside the body of the trigger we can choose to modify data and we usually do. In this example, I'll be of using a trigger to enforce a data integrity rule. The rule states that we cannot ever delete a category. We must just mark that category as inactive.

So if someone tries to delete the category, I want to trigger to block the action and instead update the record and set active equal to 0. I staged some code for you in your exercise file. Let's talk about this code. CREATE TRIGGER CategoryDelete on (dbo).(Categories) and line 3 says INSTEAD OF DELETE. So again that will prevent the DELETE statement from happening. Line 6, 7, and 8 perform an update on the categories table instead of the delete.

It's going to set active equal to 0 where the category is in and then we select from the deleted table. The deleted table is a temporary table automatically created by the trigger that contains the data the user was trying to delete. So let's go ahead and run this. Command successful. We can refresh our trigger section and we should see CategoryDelete. That's good news. Now let's test it. We can select from our categories table and see what it looks like now.

And we see category number 2 Pants is currently marked as active. Let's see what would happen if someone tried to delete that category. What should've happened is the trigger should've caught this DELETE statement, blocked the DELETE statement, and turned it into an update instead. That appears to be exactly what happened. Category two is still there. It has not been deleted it, but instead the trigger marked it as inactive. It certainly looks like success.

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This video is part of

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  1. 2m 15s
    1. Welcome
      51s
    2. What you should know
      51s
    3. Using the exercise files
      33s
  2. 11m 1s
    1. Comparing triggers, functions, and procedures
      3m 25s
    2. Why use a stored procedure?
      4m 59s
    3. Why use functions?
      1m 27s
    4. Why use triggers?
      1m 10s
  3. 6m 2s
    1. Configuring your environment
      4m 53s
    2. Downloading and installing a sample database
      1m 9s
  4. 26m 25s
    1. Creating a stored procedure
      2m 46s
    2. Modifying a stored procedure
      2m 34s
    3. Returning data using data sets
      3m 45s
    4. Returning data using cursors
      3m 45s
    5. Using input and output parameters
      5m 24s
    6. Using security and permissions
      5m 24s
    7. Using transactions
      2m 47s
  5. 11m 56s
    1. Creating a user-defined function
      4m 59s
    2. Exploring single-value functions
      4m 18s
    3. Exploring table value functions
      2m 39s
  6. 9m 31s
    1. Using "after" triggers
      3m 47s
    2. Using "instead of" triggers
      2m 9s
    3. Using nested triggers
      1m 38s
    4. Using database-level triggers
      1m 57s
  7. 12m 43s
    1. Exploring a real-world INSERT procedure
      5m 32s
    2. Exploring a real-world UPDATE procedure
      3m 13s
    3. Implementing logging on DELETE
      3m 58s
  8. 19m 38s
    1. Understanding the Common Language Runtime (CLR) and the .NET framework
      1m 52s
    2. Using CLR with SQL Server 2012
      4m 11s
    3. Writing stored procedures with C# .NET
      5m 51s
    4. Writing functions with .NET
      5m 7s
    5. Choosing between T-SQL vs. CLR
      2m 37s
  9. 11m 34s
    1. Creating a basic web form and connecting to a database
      2m 56s
    2. Executing a stored procedure
      2m 4s
    3. Passing parameters
      3m 41s
    4. Getting return values
      2m 53s
  10. 1m 43s
    1. Next steps
      1m 43s

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