DATEDIFF(类型，开始时间，结束时间）
DATEADD(类型，时间间隔，时间)
CAST(数据 as 转换类型)
DATEDIFF(HOUR,DATEADD( HOUR,sf.kaiShiShiJian_hour , CAST( sf.kaiShiShiJian_date AS DATETIME) ), DATEADD( HOUR,sf.jieShuShiJian_hour , CAST(sf.jieShuShiJian_date AS DATETIME) )) chiXvShiJian,