MYSQL
(quick examples)
ASSUMING ONLY 1 TABLE & COLUMN SELECT `COLUMN` FROM `TABLE` GROUP BY `COLUMN` HAVING COUNT(*)>1
SELECT `COLUMN`, COUNT(*) AS `ROWS` FROM `TABLE` GROUP BY `COLUMN` HAVING `ROWS` > 1
SELECT * FROM `TABLE` WHERE `COLUMN` IN ( SELECT `COLUMN` FROM `TABLE` GROUP BY `COLUMN` HAVING COUNT(*) > 1 )