data aaa;
input x $ @@;
cards;
a a s s d d f f d s d a f s d a f s
;
run;

data tmp;
input x $ @@;
id=_n_;
cards;
a d s f
;
run;

proc sql;
create table bbb as
select t.x from
aaa t
inner join
tmp t1
on t.x=t1.x
order by t1.id;
quit;

这个算不算辅助变量？

you can define a auxiliary variable as below and sort by that auxiliary variable.

proc format ;
value $myorder
a=1
d=2
s=3
f=4
;
run;

data aaa;
input x $ @@;
xorder=put(x, $myorder.);
cards;
a a s s d d f f d s d a f s d a f s
;
run;

proc sort data=aaa; by xorder; run;

proc print;run;

Yes. Auxiliary variable must be the effectively way to deal with the problem. But I only wonder if here exist another directly way, such a proc stop, a option in proc sort, to solve this problem.

{:3_42:}