SQL日期相减

cast(datediff(HOUR,substring(dyrq,1,4) + '-' + substring(dyrq,5,2) +'-'+substring(dyrq,7,2) +' '+ substring(dyrq,9,2) +':'+ substring(dyrq,11,2) +':'+ substring(dyrq,13,2), substring(dyrq,1,4) + '-' +substring(a.auditdate,5,2) + '-'+substring(a.auditdate,7,2)+' '+ substring(a.auditdate,9,2) +':'+ substring(a.auditdate,11,2) +':'+ substring(a.auditdate,13,2)) as decimal(15,2))