mysql选择datetime字段小于指定值的所有记录

So I am trying to run a query that will select, in this case, clients that haven't had an appointment is X amount of time (2 weeks for instance). It boils down to "show me a list of clients that haven't had an appointment in 2 weeks". I'm attempting to solve this in php by doing something like:So I am trying to run a query that will select,