Solved

how do I write a single column trigger?

Posted on 2003-12-02
3
213 Views
Last Modified: 2010-08-05
I want to know how to write a trigger so that it fires only after a column value has been changed from a 0 to a 1?

0
Comment
Question by:jayrod
3 Comments
 
LVL 26

Accepted Solution

by:
Hilaire earned 400 total points
ID: 9859063
create trigger <triggername> on <tablename>
for update
as
if update(<yourcolumn>)
begin
   update whatever you want from <tablename> a inner join inserted b
   on <tablename>.key = inserted.key
   where inserted.<yourcolumn> = 1

end

the if update(<yourcolumn>) will ensure that the inner code is executed only if <yourcolumn> is updated

don't forget that the inserted table may have several rows (case of a massive update eg)
the where clause will allow you to make changes only if the value in <yourcolumn> has been set to 1

Hilaire



0
 
LVL 19

Assisted Solution

by:Dexstar
Dexstar earned 100 total points
ID: 9860455
@jayrod:

> I want to know how to write a trigger so that it fires only after a column
> value has been changed from a 0 to a 1?

Hilaire got you most of the way there, but if you want it to only execute when a column was changed from a 0 to a 1, then you'll need something more like this:
     CREATE TRIGGER YourTable_UpdateTrigger ON YourTable
     FOR UPDATE
     AS
     IF UPDATE( TheColumn )
     BEGIN
          IF ( EXISTS(SELECT * FROM Inserted I INNER JOIN Deleted D ON I.PK = D.PK WHERE D.TheColumn = 0 AND I.TheColumn = 1) )
          BEGIN
               /* Do what you wanted to do here */
          END
     END

I guess I need to know more about WHAT you want to do when the field changes to write it any better than that.

Hope That Helps,
Dex*
0
 
LVL 8

Expert Comment

by:Dishan Fernando
ID: 9864215
IF EXISTS (SELECT * FROM sysobjects WHERE type = 'TR' AND name = 'TrggerName')
      BEGIN
            PRINT 'Dropping Trigger TrggerName'
            DROP  Trigger TrggerName
      END
GO

PRINT 'Creating Trigger TrggerName'
GO

CREATE Trigger TrggerName
      ON TableName
FOR UPDATE

AS

      INSERT INTO OtherTable(col,col...) -- OR Do what ever u want
      FROM
            Inserted
      WHERE  
            OneZeroChangeCol = 1

GO


0

Featured Post

Best Practices: Disaster Recovery Testing

Besides backup, any IT division should have a disaster recovery plan. You will find a few tips below relating to the development of such a plan and to what issues one should pay special attention in the course of backup planning.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

JSON is being used more and more, besides XML, and you surely wanted to parse the data out into SQL instead of doing it in some Javascript. The below function in SQL Server can do the job for you, returning a quick table with the parsed data.
I have a large data set and a SSIS package. How can I load this file in multi threading?
This videos aims to give the viewer a basic demonstration of how a user can query current session information by using the SYS_CONTEXT function
Via a live example, show how to setup several different housekeeping processes for a SQL Server.

808 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question