如何将观测号（即行号）作为sql select的限定条件

shiyiming

语句如下：

proc SQL;
create view ynb2.count5 as
          select '最近1年内' as tenor, count3_z.COL1 as CDL from ynb2.count3_z where obs=1
    union all select '最近6月内' as tenor, count3_z.COL1 as CDL from ynb2.count3_z where obs=2
    union all select '最近3月内' as tenor, count3_z.COL1 as CDL from ynb2.count3_z where obs=3
    union all select '最近1月内' as tenor, count3_z.COL1 as CDL from ynb2.count3_z where obs=4;

本想以为观测号OBS=可以作为条件，但运行不了

请指教，用观测号作为限定条件应该怎么写

shiyiming

data ynb2.count5;
        set ynb2.count3_z;
        if _n_ in (1,2,3,4) then
        output;
run;

shiyiming

replace 'obs' with 'monotonic()'