Re: after delete trigger behavior

Stephan Szabo <sszabo@megazone.bigpanda.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'sgrouping 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