%macro substractcol;
    proc sql noprint;

    select count(distinct id) into :cnt from mydata;

quit;

%let cnt=%eval(&cnt);

proc sql noprint;

    select  distinct id into :id_1-:id_&cnt. from mydata;
        quit;
    data myfinal;

    set mydatal;

keep &id_1-&&id_&n.;  /*该行需要怎么写，想要保存宏变量保存的列名*/

run;  
%mend substractcol;
%substractcol;