Question

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:

CREATE OR REPLACE TRIGGER ZERO_COPIES_TRIGGER
after
update of counter_attribute
on my_table
referencing new as new
for each row when(new.copies < 0)
begin
  delete from my_table where my_table.id = :new.id;
end;

Answer 1

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.