select t.* from (select T_EMP.*,CONVERT(datetime,CONTRACTEND,20) END1 from T_EMP where CONTRACTSTART is not null and CONTRACTEND is not null and CONTRACTEND not like'无固定%') t WHERE t.CONTRACTSTART BETWEEN DATEADD(YEAR,-6,t.END1) AND DATEADD(YEAR,-1,t.END1)

无固定后面t是啥？