data m(index=(id));set modify.m;run;
data m;
set modify.n;
modify m key=id;
if _IORC_=%sysrc(_sok) then
do;b=b;
replace;
end;
else
if _IORC_=%sysrc(_dsenmr) then
do;
output;
_error_=0;
end;
run;
proc print data=m;
run;
不明白这个程序的意思？求大神指导