什么数据库?
select '75.8时' as "原始",case when replace('75.8时','时','')*1<4.2 then '小于4.2' else '不小于4.2小时' end as tt from dual
select '75.8时' as "原始",case when replace('3.6时','时','')*1<4.2 then '小于4.2' else '不小于4.2小时' end as tt from dual