求解

proc sql;
create table NEW
as select a.*, b.YEAR - 1 as Y
from OLD as a left join LIST as b
on a.ID=b.ID and a.YEAR=b.Y;
quit;

上面的code里 LIST里面有年份 我想把年份减1然后merge回OLD 但是不好使。。。好像是b.YEAR-1不对
求教了！！谢谢！！！