Question

I’ve got a table foo with a text field bar in it. On that table I’ve got an after update trigger that is basically the following:

CREATE OR REPLACE FUNCTION update_foo() 
RETURNS TRIGGER
SECURITY DEFINER
AS
$_$
DECLARE 
BEGIN
  IF TG_OP = 'UPDATE' and NEW.bar = OLD.bar THEN
    return NEW;
  END IF;

  /* Do some stuff */

END
$_$
LANGUAGE PLPGSQL;

Then I do something like this: Update foo set bar = bar || '';.

But it doesn’t bail when the text values are equal.

My question is why wouldn’t PostgreSQL 8.3, and specifically pl/PgSQL call them equal and bail out early?

Disclaimer: Table, field, and variable names have been changed from their original to allow for posting online.

Answer 1

It Would be because one of the values is a null.
and a null cannot be equal to any other value,

So you will need to add the extra criteria

(New.bar is  null or Old.bar is null)

Or

  NEW.bar is not distinct from OLD.bar