Trying to capture Date and time when a specific field in a single record is updated - sql

Question

I had to add the fields Comments and Comments DateTime to a table. A user would leave comments, and when this was complete, the Comments DataTime is supposed to capture the date and time of the update of the Comments field. Many examples I've seen track when the entire record updates a datetime field, however I'm looking to capture the datetime only when the specific Comments field is update for that record. How do I go about doing this? Any advice is greatly appreciated.
edit Getting incorrect syntax near the keyword 'FROM'
CREATE TRIGGER dbo.updateComments
ON dbo.tbl_location_history
/*Check whether column comments has been updated. If column comments has
been changed, update column comments_datetime with getdate().*/
FOR INSERT,UPDATE AS
/*Use IF (COLUMNS_UPDATED() &7) = 7 to see whether column 7 was updated.*/
/*Checking out IF UPDATE(comments) for proper time stamp */
IF UPDATE(comments)
BEGIN
SET NOCOUNT ON;
UPDATE dbo.tbl_location_history
SET dbo.tbl_location_history.comments_datetime = GETDATE();
FROM table dbo.tbl_location_history INNER JOIN
inserted i ON dbo.tbl_location_history.location_id = i.id
END

Answer 1

I would create a trigger on sql server. In that trigger test if the comment is different than the old record. You can log the activity anywhere you like using code in the trigger.

Answer 2

If you want to track when ONLY the comments field is updated you can use the COLUMNS_UPDATED() function in your update trigger. It can be used to track if column 1, 4, and 6 were updated, or it can track if only column 10 was updated. The code to put inside your trigger will look something like this:
IF CAST(SUBSTRING(COLUMNS_UPDATED(),1,1) AS INT) = 0)
BEGIN
--do something here
END
It's kind of confusing, but it basically checks which columns were updated and uses binary (I think) to denote what columns were actually changed. Please read through this MSDN article and let me know if you have specific questions.
https://msdn.microsoft.com/en-us/library/ms186329.aspx

Answer 3

An alternative to tracking these changes in your own schema is to configure the database to do it for you. Starting with SQL Server 2008, you can enable change tracking at the database level. Change tracking is like an index in that it is maintained transparently by SQL Server. Once enabled on a table, a variety of change tracking functions are available that let you inspect what changed and when.

Answer 4

GOT IT! First off, thank you to EVERYONE that posted here. You've been an amazing help directing me in the right direction. Looked over the code and saw my mistakes (good night's sleep does wonders). Here's the solution:
CREATE TRIGGER dbo.updateComments
ON dbo.tbl_location_history
/*Check whether column comments has been updated. If column comments has
been changed, update column comments_datetime with getdate().*/
FOR INSERT,UPDATE AS
/*Use IF (COLUMNS_UPDATED() &7) = 7 to see whether column 7 was updated.*/
/*Checking out IF UPDATE(comments) for proper time stamp */
IF UPDATE(comments)
BEGIN
SET NOCOUNT ON;
UPDATE dbo.tbl_location_history
SET dbo.tbl_location_history.comments_datetime = GETDATE()
FROM dbo.tbl_location_history INNER JOIN inserted i ON dbo.tbl_location_history.location_id = i.location_id
END