Thank you all for the valuable replies.
I've also got suggestions to use IS NOT DISTINCT FROM or STRICT at http://stackoverflow.com/questions/35742865/how-to-ensure-that-a-stored-function-always-returns-true-or-false
but the former has the edge case of NULL=NULL returning TRUE
and with the latter I would have to be careful with the way I call my function -
and I am worried I might forget it later and this is a security related...
So I will probably use this function:
CREATE OR REPLACE FUNCTION check_user(in_social integer,
in_sid varchar(255),
in_auth varchar(32))
RETURNS boolean AS
$func$
SELECT CASE
WHEN in_social IS NULL THEN FALSE
WHEN in_sid IS NULL THEN FALSE
WHEN in_auth IS NULL THEN FALSE
ELSE (MD5('secret word' || in_social || in_sid) = in_auth)
END;
$func$ LANGUAGE sql IMMUTABLE;
Regards
Alex
