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Using "after" triggers

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

Video: Using "after" triggers

In this chapter, I'll be working with two new tables; a products table and a categories table. I've created a script that will generate those tables and populate them with some data. There in your exercise files. You can copy and paste all of that into Management Studio and run it. And it should've given me two new tables. And let's double check and make sure we have some data in those tables. Oh, that looks good. The first type of trigger I'd like to talk about is called an 'after' trigger.

Using "after" triggers

In this chapter, I'll be working with two new tables; a products table and a categories table. I've created a script that will generate those tables and populate them with some data. There in your exercise files. You can copy and paste all of that into Management Studio and run it. And it should've given me two new tables. And let's double check and make sure we have some data in those tables. Oh, that looks good. The first type of trigger I'd like to talk about is called an 'after' trigger.

It's called this because it executes immediately after an insert, update or DELETE statement. The trigger allows the original statement to occur with no modifications. Then it immediately takes over and starts doing some work. In this example, we're going to use the trigger to enforce a business rule. The business rule states that whenever a category is marked as inactive, all of the products in that category should immediately be marked as inactive also. So I have some code staged for this in your exercise files.

Just like with functions and stored procedures, we start with the keyword Create and then we use the keyword Trigger. Then we have to give it a name. I called mine CategoryDeactivation. Line 2, we are setting a relationship with a table. Every 'after' trigger is related to one table and is going to react to actions only on that table. Line 3 says AFTER UPDATE. So that's the one verb I'm interested in. This trigger will ignore, insert and DELETE statements. It will only run immediately after an UPDATE statement.

Then let's look at the bulk of the code; line 6 through 14. We start off on line 6 creating a variable to hold the isActive bit. I want to make sure with the update that came in, was someone trying to set a category as active or trying to set it as inactive. So on line 11 there, I'm looking at the isActive bit in saying it whether or not it is equal to zero. If it is in fact equal to zero, I'll perform the actions that start on line 12 which is UPDATE Products.

Set active equal to zero and then we are saying where category ID is in the category ID from inserted. Notice there on the line 14, where you are querying in a table called inserted. Inserted is a temporary table that's only available inside of the trigger. It's automatically created by the machine and it holds all of the new information that someone is trying to put into the table. So let's go ahead and run this, command(s) completed successfully. That's good.

And now we should be able to go under the categories table and see a new trigger. And there it is, CategoryDeactivation. So to test this, let's first look again at the products table, and we see three items in category one all of them are active. Now I'm going to issue a command that will mark the category one as inactive. When I execute this, it should perform that action and then the trigger will fire and update the product table, and mark everything in category 1 as inactive.

That would appear to be successful. Let's look at the product table just to make sure. And yes, our three products in category 1 are now inactive. We use the trigger to enforce the business rule that whenever a category is marked inactive all of the products should immediately be marked as inactive also.

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This video is part of

Image for SQL Server: Triggers, Stored Procedures, and Functions
 
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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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