Trying to omit duplicate rows in a UNION

Question

I am trying to omit duplicate rows from my union’ed join of 2 tables but am running into a problem which I am hoping someone can help me with. The following SQL works, but doesn’t omit the dups.
SELECT service_code, description_txt, effective_date, ROW_NUMBER() OVER (PARTITION BY service_code
ORDER BY effective_date DESC) AS rn
FROM
(SELECT s.service_code, s.effective_date, s.description_txt
FROM state_code_desc s
WHERE s.expire_date IS NULL
AND s.code_type='H'
AND s.coverage_type='W'
AND s.geo_area_code='USA'
AND s.state_abbr='GE'
UNION
SELECT f.service_code, f.effective_date, f.description_txt
FROM fed_code_desc f
WHERE f.code_type='H'
AND f.expire_date IS NULL
ORDER BY service_code
When I try to add the WHERE RN=1 immediately before the ORDER by service_code (last line of the SQL), I get the following error:
ORA-00904 – “RN” Invalid identifier
Can someone out there help me out, please?
Thanks!
Janet
P.S.-I'm running Oracle 9.1

Answer 1

Just a precesion,
It is not a question of analytic functions at all
In fact, column aliases are not usable in tbe same
query in the WHERE clause.
SQL> SELECT deptno,COUNT(*) OVER (PARTITION BY deptno) cnt
  2  FROM emp;
    DEPTNO        CNT
        10          2
        10          2
        20          2
        20          2
        30          5
        30          5
        30          5
        30          5
        30          5
9 rows selected.
SQL> SELECT deptno,COUNT(*) OVER (PARTITION BY deptno) cnt
  2  FROM emp
  3  WHERE cnt=1;
WHERE cnt=1
ERROR at line 3:
ORA-00904: "CNT": invalid identifier
SQL> SELECT deptno,sal*100 s,COUNT(*) OVER (PARTITION BY deptno) cnt
  2  FROM emp
  3  WHERE s=100;
WHERE s=100
ERROR at line 3:
ORA-00904: "S": invalid identifier
SQL> SELECT deptno,sal*100 s,COUNT(*) OVER (PARTITION BY deptno) cnt
  2  FROM emp
  3  WHERE (sal*100)=100;
no rows selected
SQL> SELECT deptno,sal*100 s,COUNT(*) OVER (PARTITION BY deptno) cnt
  2  FROM emp
  3  HAVING COUNT(*) OVER (PARTITION BY deptno)=2;
HAVING COUNT(*) OVER (PARTITION BY deptno)=2
ERROR at line 3:
ORA-30483: window  functions are not allowed hereKhurram