Re: after delete trigger behavior

Stephan Szabo <sszabo(at)megazone(dot)bigpanda(dot)com> writes:
> Is there anything we have right now that will handle this kind of thing
> without requiring either updating all the counts after a deletion in a
> statement trigger or once per row updating all the counts for records with
> the same "a" (doing something like make a sequence and using it in a
> subselect matching keys)?

The best thing I can think of is your first idea, ie, renumbering all
the rows in a statement-level AFTER DELETE trigger. Something like
(untested)

DECLARE
rec record;
n integer := 1;
BEGIN
FOR rec IN
SELECT * FROM table
WHERE <<grouping cols = rec's grouping cols>>
ORDER BY sort_order
LOOP
IF rec.sort_order != n THEN
UPDATE table SET sort_order = n
WHERE <<primary key = rec's primary key>>;
END IF;
n := n + 1;
END LOOP;
END;

Ugly as this is, it's at least linear in the number of rows to be
changed; the originally proposed trigger was O(N^2) in the number of
rows affected, and would surely be intolerably slow for multiple deletes
in a reasonably sized table. Given an index on the grouping columns
plus sort_order, it could even be reasonably fast (don't forget to make
the ORDER BY match the index).

regards, tom lane