If the Invoices.PaymentTotal column changes during an update, I wanted the trigger to detect the change and then copy the Vendor's Name, and Address to another table from the Vendors table for the vendor for that same invoice.

>With triggers, I don't believe you can.

>Closest you can do is the following....suppose you want to detect if ProductMaster.ListPrice has changed...

DECLARE @NumRowsChangedByUpdate int

SET @NumRowsChangedByUpdate = 
    (select  Count(ProductMaster.ProductKey) from ProductMaster
                                         JOIN Inserted on ProductMaster.ProductKey = Inserted.ProductKey
                                         join Deleted on ProductMaster.ProductKey = Deleted.ProductKey
                                                where Inserted.ListPrice <> Deleted.ListPrice)

if @NumRowsChangedByUpdate > 0
          -- then go do something

However, if you're using Change Data Capture, you could theoretically tap into something using CDC if you set it up for just a single column, though it's going to involve some work.

What specifically do you want to do when the single column value changes?