在SQL Server中创建触发器

Question

I got lost when I wanted to create trigger using the pre-defined "CREATE TRIGGER" of SQL Server 2008 R2. Could you please give me a direct SQL statement that I can use to create a trigger, and tell me how to define AFTER, BEFORE, and all that?

Also, how can I know the rows UPDATED/INSERTED/DELETED, and use their column values to do operations inside the trigger?

Answer 1

The basic syntax is

CREATE TRIGGER YourTriggerName ON dbo.YourTable
FOR|AFTER INSERT, UPDATE, DELETE
AS
BEGIN
     /*Put what ever you want here*/
     UPDATE AnotherTable
          SET SomeColumn = AnotherColumn
     FROM inserted | deleted
END
GO

Answer 2

Databases are set-oriented and triggers are no different. A trigger will fire when a given operation is performed and that operation might affect multiple rows. Thus, the question "Say I want to know the Primary Key of that row" is a misnomer. There could be multiple rows inserted.

SQL Server provides two special tables for AFTER triggers named inserted and deleted which represent the rows that were inserted or deleted by an action and are structured identically to the table being affected. An update trigger might populate both inserted and deleted whereas an insert trigger would only populate the inserted table.

From comments:

but the email recipient will be decided based on a value in a second table, where the foreign key ID is located in the first table (which is the one with trigger

The answer to this question is to use the inserted table (which again, you must assume could have multiple rows) to cycle through the rows and send an email. However, I would recommend against putting email logic in a trigger. Instead, I would recommend putting that logic in a stored procedure and send your email from that.

For reference: Create Trigger

Answer 3

A trigger is an event-based process that is "triggered" after a table is changed in some way. This will be on DELETE, UPDATE, INSERT, and so forth. Your BEFORE and AFTER syntax will define whether to run the trigger before or after the event is committed.

That's the short version. Check out MSDN .