proc sql;
select no,time,avg(x) as avg from aaa  group by no,time;
quit;

proc sql noprint;
create table want as
select no,time,mean(x) as mean from have group by no,time order by no,time;
quit;

proc sql noprint;
create table want as
select no,time,mean(x) as mean from have group by no,time order by no,time;
quit;

都是用SQL的 提供一个data步的思路

data bbb(keep=no time mean);
set aaa;
by no time;
if first.no and first.time then do; num=0; total=0; end; /*防止上一号最大time与下一号最小time相同*/
if first.time then do; num=0; total=0; end;
total+x;
num+1;
if  last.time then do;
mean=total/num; output;
end;
run;