In SQL Server 2008, I have a scenario where I have a table with complex validation upon insert / update. This includes needing to temp convert an XML input into a table in order to validate its data against a permanent table.
However, I also have the scenario where I will often update simple integer columns that require no validation. From what I have read here, it seems that SQL Server is going to return the entire row in the temp in-memory “inserted” table, not just the affected columns, when I perform an update. If this is so, then it means for every simply integer update I perform, complex XML validation will be needlessly done.
Do I understand this correctly and if so, how do I get around this short of requiring inserts / updates via a stored proc?
Yes, first off, the triggers will fire for EVERY INSERT or UPDATE operation – you cannot limit that to only fire when certain columns will be affected. You can check inside the trigger to see whether or not certain columns have been affected and make decisions based on that – but you cannot prevent the trigger from firing in the first place.
And secondly, yes, when the trigger fires, you will have ALL columns of the underlying table in the INSERTED and/or DELETED pseudo tables.
One way you might want to change this is by moving the large XML column into a separate table and put that big heavy XML validation trigger only on that table. In that case, if you update or insert into the base table only, you’ll get less data, less validation logic. Only when you insert or update into the XML table, you’ll get the whole big validation going.