NULL != text ?

I was trying this:

IF (OLD.value != NEW.value) THEN
--
END IF;

and couldn't get the condition to evaluate to true at
all if OLD.value was NULL. I also tried:

IF (OLD.value NOT LIKE NEW.value) THEN
--
END IF;

with the same result. But this works:

IF ((OLD.value is NULL and NEW.value is NOT NULL) or
(OLD.value != NEW.value)) THEN
--
END IF;

So, does NULL != 'abc' always evaluate to false? The
manual
(http://www.postgresql.org/docs/8.0/interactive/functions-comparison.html)
states don't compare NULL values using =, but nothing
about using !=

CSN

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