query question

I am new to using postgresql and have the following question. if i submit
a query (through a perl script), what values (and in what order) will be
returned to me? here is my query:

SELECT p.ids_name, m.start_time, m.end_time
FROM mail_schedule m, personnel p
WHERE p.ids_int = m.ids_int AND
m.dow = $weekday AND
$timestamp BETWEEN m.start_time AND m.end_time
UNION
SELECT p.ids_name, c.on_start, c.on_end
FROM mail_changes c, personnel p
WHERE p.ids_int = c.ids_int AND
$timestamp BETWEEN c.on_start AND c.on_end
EXCEPT
SELECT p.ids_name, c.off_start, c.off_end
FROM mail_changes c, personnel p
WHERE p.ids_int = c.ids_int AND
$timestamp BETWEEN c.off_start AND c.off_end

thanks in advance for any assistance you can provide.
chris mutchler
davron(at)leibnizcreations(dot)com