用update set实现:
data a;
input type $ initime yymmdd10. finaltime yymmdd10.;
cards;
a 2017/1/1 2017/3/1
a 2017/1/2 2017/3/2
a 2017/1/3 2017/3/3
b 2017/1/4 2017/3/4
b 2017/1/5 2017/3/5
;
run;
proc sql;
update a as a
set initime=finaltime
where type=\'a\';
quit;