SQL CASE语句

select trk,in_date,out_date,cntr,floor((out_date-in_date)*24*60) times,
case
when ((out_date-in_date)*24*60-20<0) then '20·ÖÖÓÒÔÏÂ'
when ((out_date-in_date)*24*60-20>0 and (out_date-in_date)*24*60-30<0) then '30·ÖÖÓÒÔÏÂ'
else '30·ÖÖÓÒÔÉÏ'
end time_class from traf_hist where trk_type='CY' and status<>'VD'