proc sql;
create table age_mean as
select *,
mean(age) as age_mean,/*计算全班同学的平均年龄*/
case tuanyuan when '1' then mean(age) end else . as  age_mean_tuanyuan,/*计算团员的平均年龄*/
case substr(id,9,1) when 'B' then  mean(age) else . end as age_mean_nongcun/*计算农村户口学生的平均年龄*/
case substr(id,9,1) when 'A' then  mean(age) else . end as age_mean_chengzhen/*计算城镇户口学生的平均年龄*/
from age
group by class;
quit;