OUTER JOIN vs UNION ... faster?

Got a query that looks like:

========================================================================

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send0,card_info,category_details
WHERE send0.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send1,card_info,category_details where send1.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send2,card_info,category_details where send2.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send3,card_info,category_details where send3.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send4,card_info,category_details where send4.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send5,card_info,category_details where send5.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)
FROM send6,card_info,category_details where send6.card_id=card_info.card_id
AND category_details.mcategory='e-cards'
AND card_info.main_cat=category_details.category
AND send_date >= '2001/04/08'
AND send_date <= '2001/05/14' group by 1,2

UNION ALL

SELECT card_info.main_cat, category_details.sub_cat_flag,count(*)

========================================================================

*Really* dreading the thought of changing it to an OUTER JOIN, and am
wondering if there would be a noticeable speed difference between going
from the UNION above to an OUTER JOIN, or should they be about the same?

Marc G. Fournier ICQ#7615664 IRC Nick: Scrappy
Systems Administrator @ hub.org
primary: scrappy(at)hub(dot)org secondary: scrappy(at){freebsd|postgresql}.org