SQL Server trigger to preserve an existing value

I have a database field that stores a tracking number for shipments. Occasionally we send the order out in 2 shipments. When we process the 2nd shipment, our shipping software writes the new tracking number into the tracking field removing the tracking number that was already there.
I want to know the syntax to write a trigger for SQL Server that would evaluate the TrackingNumber1 field on update and, if there was already a tracking number in TrackingNumber1, it would capture it and move it to TrackingNumber2. The final result would be that I have both tracking numbers captured and available to me.
Can this be done and how?
Thanks -
GenesisTechAsked:
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Russell FoxDatabase DeveloperCommented:
"DELETED" and "INSERTED" are what SQL Server calls the original data and the new data, respectively - they're essentially both virtual tables. This will concatenate any number of new tracking numbers as long as [TrackingNumber2] is big enough:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:		<Author,,Name>
-- Create date: <Create Date,,>
-- Description:	<Description,,>
-- =============================================
CREATE TRIGGER trgKeepTrackingNumber
   ON ShippingTable
   AFTER UPDATE
AS 
BEGIN
	SET NOCOUNT ON;

	UPDATE shp
		SET [TrackingNumber2] = [TrackingNumber2] + ', ' + old.[TrackingNumber1]
	FROM ShippingTable shp
		JOIN INSERTED new
			ON shp.[ID] = new.[ID]
		JOIN DELETED old
			ON shp.[ID] = new.[ID]
	WHERE old.[TrackingNumber1] <> new.[TrackingNumber1]


END
GO

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GenesisTechAuthor Commented:
Russell -

Awesome. Delivered as requested and as needed. THANK YOU!

I will plug this in and give it a try and get back to you.
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GenesisTechAuthor Commented:
Russell,

I do have a question that I did not think about. If we mess up the shipment and I go into the record and Delete the Tracking Number will the trigger you wrote still move the tracking number to TrackingNumber2 even though I deleted it?
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Russell FoxDatabase DeveloperCommented:
If you delete just the tracking number, i.e. clear out that field, then yes, it will add the old, deleted number to TrackingNumber2. If you delete the entire shipping record, then no, the whole record will go away. If you don't want it to add the deleted tracking number, then you can exclude that in the trigger:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- =============================================
-- Author:		<Author,,Name>
-- Create date: <Create Date,,>
-- Description:	<Description,,>
-- =============================================
CREATE TRIGGER trgKeepTrackingNumber
   ON ShippingTable
   AFTER UPDATE
AS 
BEGIN
	SET NOCOUNT ON;

	UPDATE shp
		SET [TrackingNumber2] = [TrackingNumber2] + ', ' + old.[TrackingNumber1]
	FROM ShippingTable shp
		JOIN INSERTED new
			ON shp.[ID] = new.[ID]
		JOIN DELETED old
			ON shp.[ID] = new.[ID]
	WHERE old.[TrackingNumber1] <> new.[TrackingNumber1]
		AND COALESCE(old.[TrackingNumber1], '') <> ''

END
GO

Open in new window

A word to the wise: triggers are often overlooked when someone else has to troubleshoot an issue. Make sure you document the trigger and what it does, preferably in the code you use to update the tracking number. Otherwise, people just see weird behavior and don't know why!
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Russell FoxDatabase DeveloperCommented:
Also, FWIW, it would be better to create a stored procedure that's called to update the tracking number value, and the proc can handle this rather than a trigger. That's assuming you have any control over the UI code, of course. We use a billing system that I created along with our .Net guy, and he has no SQL code other than to call stored procedures and functions that I've created.
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GenesisTechAuthor Commented:
Russell,

Excellent answer - works great. Thanks for your help!
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Microsoft SQL Server 2005

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