storing record-array in varchar?

hi list

how can something like this be achieved:

UPDATE mytable SET m_list = (SELECT DISTINCT s_id FROM sometable WHERE s_id > 6000) WHERE m_id = 10;

the field m_list would then hold something like '6001, 6002, 6003, 7000', which ideally i could later use for something like SELECT * FROM sometable JOIN mytable WHERE s_id IN m_list AND m_id = 10;

field m_list would idealy be a varchar if possible...

thanks,
thomas