MY-SQL - 시간차이 함수

datediff(시간형식,비교시간a,비교시간b)

select u_no,datediff(s,u_reg_updated,u_reg_start),* from exam_user where u_no in(
select (case when datediff(mi,u_reg_start,u_reg_updated) > 90 then u_no end) as u_no from exam_user)