-- update table with select and group by statement
-- Ohs my poor SQL.
-- contacts:beginman.cn

update group_info as g
    left join (
		select gi.group_id, count(gm.id) as nums from group_info gi
		inner join group_members gm on gm.group_id = gi.group_id
		group by gm.group_id
	)
	as m on g.group_id = m.group_id
	set g.member_count = m.nums;