proc sql noprint;
select count(distinct y) into :county from b;
quit;

%let county=&county;
%put &county; * to check the value;

proc sql noprint;
select distinct y into :y1-:y&county
from b;
quit;

%put _user_; * to check the macro values;

data new;
set a;
do i=1 to &county;
        if index(x,&&y&i) then do;
                z=trim(left(&&y&i));
                i=&county; * to leave the loop;
        end;
end;

run;

没有数据集，目前还没有验证，仅供参考