proc sort data= out= nodupkey;
by ;
run;
空的地方请自行填满。

如何显示那些重复的观测？

If the observations in your data set is no more than 10000, the following code works well. Otherwise, u have to try in HUSH.

proc sql;
        create table test02 as
        select target_key as dupkey
                from test01
                group by target_key
                having count(*) > 1.5;
quit;