data test;
input Name$ Score;
cards;
a 1
b 2
;
run;
data nobs(keep=total);
     set test nobs=total_obs;
         total=total_obs;
         output;
         stop;
run;
用nobs读取数据集观测值时为什么要先把nobs赋值给临时变量otal_obs,如果我改成以下程序的话为什么total对应的变量值变为缺失值"."了呢？求各位大神指明原委，不甚感激
data test;
input Name$ Score;
cards;
a 1
b 2
;
run;
data nobs(keep=total);
     set test;
         total=nobs;
         output;
         stop;
run;