程序一：
data x;
if _n_=1 then input x;
datalines;
1
2
3
;
run;
proc print;
run;
程序二：
data x1;
input x;
datalines;
1
2
3
;
run;
data x2;
if _n_=1 then set x1;
run;
proc print;
run;
程序三：
data x3;
if _n_=1 then input y $;
set x1;
datalines;
a
b
c
d
;
run;
proc print;
run;
程序四：
data x4;
if _n_=1;
set x1;
run;
proc print;
run;