I would like to create a trigger that will delete a row when one of its attributes becomes negative. So far I have this, but it doesn\'t appear to be valid sql:
This is not going to work. You can't perform DML on a table which is being manipulated by a row-level trigger. You will get a "mutating table" error.
To get the result you want, your best bet is to have a flag or indicator column to identify that the record is to be deleted. Then, have a separate job or process or whatever to actually perform the delete.