data a;
input a b;
cards;
1 20
2 20
4 30
6 90
;
run;

data b(drop=i);
do i=1 to 6;
a=i;
b=.;
output;
end;
run;

proc sql;
create table c as
select b.a as ca
      ,case
      when a.b ne . then a.b
      else b.b end as cb
      from b left jion a
      on b.a=a.a
      order by b.a;
      quit;

嗯~~~excellent，我就没想到这样做！！

data a;
input a b;
cards;
1 20
2 20
4 30
6 90
;
run;

data work.b;
        do a = 1 to 6;
                outpaut ;
        end;
run;

data work.c;
        merge work.a work.b;
        by a;
run;

需要先按照a排好序

此处正当用merge by，sql略显累赘