SQL equivalent

[G_I_Jeff]

DATA TABLE1;
 SET TABLE2
     TABLE3
     TABLE4;
 KEEP OBS2 OBS4;
RUN;

[Steelers_In_DC]

Union All will include duplicates.  Union will remove duplicates:

proc sql;
create table table1 as
select obs2,obs4
from table2
union
select obs2,obs4
from table3
union
select obs2,obs4
from table4;