也可以，我不习惯用means而已
修改如下
/*按企业名和时间排序*/
proc sort data=a;
by coname date;
run;
/*将各企业按时间计数*/
data a;
set a;
by coname date;
if first.coname then n1=1;
else n1+1;
run;
/*计算各企业的最大笔数*/
proc sql;
create table b as
select distinct *,max(N1) as nn
from a group by coname;
quit;

/*取最大笔数大于5的前5年数据*/
proc sql;
create table c as
select *
from b
where nn>5 and n1<6;
quit;
/*求中位数*/
proc means data=c;
var dp;
by coname;
output out=d median=med;
run;

如果只求前五年的中位数，那就简单了
以DP为例，将前五年的数据排序，取第三行的就是中位数了

/*按企业名和时间排序*/
proc sort data=a;
by coname date;
run;
/*将各企业按时间计数*/
data a;
set a;
by coname date;
if first.coname then n1=1;
else n1+1;
run;
/*计算各企业的最大笔数*/
proc sql;
create table b as
select distinct *,max(N1) as nn
from a group by coname;
quit;

/*取最大笔数大于5的前5年数据*/
proc sql;
create table c as
select *
from b
where nn>5 and n1<6;
quit;
/*按企业名和DP排序*/
proc sort data=c;
by coname dp;
run;
/*各企业分类计数*/
data c;
set c;
by coname dp;
if first.coname then n2=1;
else n2+1;
run;
/*去第三笔即为中位数*/
data d;
set c;
where n2=3;
drop n1 n2;
run;

如果只求前五年的中位数，那就简单了
以DP为例，将前五年的数据排序，取第三行的就是中位数了

/*按企业名和时间排序*/
proc sort data=a;
by coname date;
run;
/*将各企业按时间计数*/
data a;
set a;
by coname date;
if first.coname then n1=1;
else n1+1;
run;
/*计算各企业的最大笔数*/
proc sql;
create table b as
select distinct *,max(N1) as nn
from a group by coname;
quit;

/*取最大笔数大于5的前5年数据*/
proc sql;
create table c as
select *
from b
where nn>5 and n1<6;
quit;
/*按企业名和DP排序*/
proc sort data=c;
by coname dp;
run;
/*各企业分类计数*/
data c;
set c;
by coname dp;
if first.coname then n2=1;
else n2+1;
run;
/*取第三笔即为中位数*/
data d;
set c;
where n2=3;
drop n1 n2;
run;

如果不限定是前5年取中位数，就是说年数不定的话
可在proc sql中自己写公式，稍微复杂

不能直接求各个企业前五年的 中位数
然后再把这些中位数从大到小 排序吗？
（恕我愚钝~问的问题白痴 也不要嘲笑噻~）