I have a situation where I have a table with this structure:

ID (PK)
ParentID (FK)
PercentOwnership - Decimal (2,2)

I want to check when an item is inserted or updated in this table that the sum of all PercentOwnership fields with the same ParentID doesn't go over 1. I'm assuming I want to use a trigger here and wanted to make sure I was going down the right path (I'm a newbie with triggers). Is this right? Or is there a better way to do this?