Question

I have the following 2 tables:

items:
 id int primary key
 bla text

events:
 id_items int
 num int
 when timestamp without time zone
 ble text
 composite primary key: id_items, num

and want to select to each item the most recent event (the newest ‘when’).
I wrote an request, but I don’t know if it could be written more efficiently.
Also on PostgreSQL there is a issue with comparing Timestamp objects:
2010-05-08T10:00:00.123 == 2010-05-08T10:00:00.321
so I select with ‘MAX(num)’
Any thoughts how to make it better? Thanks.

SELECT i.*, ea.* FROM items AS i JOIN
( SELECT t.s AS t_s, t.c AS t_c, max(e.num) AS o FROM events AS e JOIN
( SELECT DISTINCT id_item AS s, MAX(when) AS c FROM events GROUP BY s ORDER BY c ) AS t
ON t.s = e.id_item AND e.when = t.c GROUP BY t.s, t.c ) AS tt
ON tt.t_s = i.id JOIN events AS ea ON ea.id_item = tt.t_s AND ea.cas = tt.t_c AND ea.num = tt.o;

EDIT: had bad data, sorry, my bad, however thanks for finding better SQL query

Answer 1

SELECT  (i).*, (e).*
FROM    (
        SELECT  i,
                (
                SELECT  e
                FROM    events e
                WHERE   e.id_items = i.id
                ORDER BY
                        when DESC
                LIMIT 1
                ) e
        FROM    items i
        ) q