【sas proc sql】coalesce

data mylearn.coalesce;
    input a $ 1-1 b $ 3-3;
    datalines;
a e
b  
c f
d g
  h
    ;
run;
proc sql feedback;
    select coalesce(a,b) from mylearn.coalesce;
quit;
proc print data=mylearn.coalesce;
run;

coalesce函数返回参数里面的第一个非空值。