proc sql noprint;
        create table bbb as
select distinct id,trt,count( case when x in (3 4) then id else . end) as tag
from aaa group by id trt order by id trt;
quit;

proc sql noprint;
        create table bbb as
select distinct id,trt,count( case when x in (3 4) then id else . end) as tag
from aaa group by id,trt order by id,trt;
quit;
程序缺了两个逗号。
但结果和我的要求不一样

在楼上的基础上增加一步就可以了~
proc sql noprint;
        create table ccc as
        select distinct id ,trt,count(case when x in (3 4) then id else . end) as x1 from aaa
        group by id,trt;
quit;

data ddd;
        set ccc;
        if x1 = 0 then tag = 0;
        else tag = 1;
        drop x1;
run;

data b;
        set aaa;
        by id;
        retain tag;
        if first.id then tag=0;
        if x in (3,4) then  tag=1;
        if last.id;
run;