SELECT * FROM table_name WHERE date_field >= NOW();
select *
from dbo.March2010 A
where A.Date >= '2010-04-01'
SELECT * FROM wp_osd_properties WHERE `listing_expiration` < '2020-08-05'
SELECT *
FROM Users
WHERE member_since < '2011-12-25'
ALTER TABLE yourTable
ADD CONSTRAINT yourDateTimeColumn CHECK (yourDateTimeColumn < GetDate() );