Re: Removing redundant itemsets

> -- Find any `a' for which `item_from_a_is_in_b' is
> -- true for all items in `a'
> SELECT a_tid AS is_redundant, b_tid AS contained_by
> FROM (
> -- For every item in every pair of purchases,
> -- determine whether the item in purchase `a'
> -- was also in purchase `b'.
> SELECT
> a.tid AS a_tid,
> b.tid AS b_tid,
> a.item AS item,
> EXISTS(
> -- Was this item from `a' also in the `b' purchase?
> SELECT 1 FROM togo x WHERE x.tid = b.tid AND x.item = a.item
> ) AS item_from_a_is_in_b
> FROM togo a INNER JOIN togo b ON (a.tid <> b.tid)
> GROUP BY a.tid, b.tid, a.item) AS item_containment
> GROUP BY a_tid, b_tid
> HAVING every(item_from_a_is_in_b);

That really should've been written as:

SELECT
a.tid AS is_redundant,
b.tid AS contained_by
FROM togo a INNER JOIN togo b ON (a.tid <> b.tid)
GROUP BY a.tid, b.tid
HAVING
EVERY(EXISTS(
SELECT 1 FROM togo x WHERE x.tid = b.tid AND x.item = a.item
));

... but I'm a bit of an idiot, and couldn't figure out why the
EVERY(EXISTS(subq)) wasn't working when testing it before.

Sorry for all the noise.

--
Craig Ringer