下面这个data例子中set flow语句是什么意思?
data new1(drop=z);
set flow;
run;
data new2(keep=x);
set flow;
run;
data new3(label='the new3 dataset');
set flow;
run;
data new4(rename=(x=xx y=yy));
set flow;
run;
proc print data=new1;
run;
proc print data=new2;
run;