data nvic;
input nvic $;
cards;
JIE09G
JIE10A
JIE11A
JIF09G
;
run;
proc sort data=nvic;
by nvic;
run;
　
data nvic1;
set nvic;
by nvic;
if first.nvic then output;
　
　
data add_symbol;
set nvic1 end=last;
if last
then
nvic=trim("'")||trim(nvic)||trim("'");
else
nvic=trim("'")||trim(nvic)||trim("'")||trim(",");
run;

为什么最后没有逗号显示，谢谢？