php, mysql How to do a random selection and limit response?

greetings, I would like to do a random selection in mysql [select * from members order by rand() limit $limit] and then I'd like to insert the items selected into a table [named already_selected] with a datetime stamp to make sure one item is only sleceted once over a defined period of time. Would it be best to do the select and then an insert? Would it be best to do a left join in The select statement? Can anyone suggest a more efficient way? Thanks, Leonard Burton