intersection.sql

SELECT user_id
FROM  `facebook_active_user_201303`
WHERE page_id =  '145649977189'
AND startdate =  '2013-03-01'
AND period =  'month'
AND user_id
IN
(
SELECT user_id
FROM  `facebook_active_user_201303`
WHERE page_id =  '152341009257'
AND startdate =  '2013-03-01'
AND period =  'month'
)

union.sql

SELECT user_id
FROM  `facebook_active_user_201303` 
WHERE (
page_id =  '145649977189'
OR page_id =  '152341009257'
)
AND startdate =  '2013-03-01'
AND period =  'month'