Why doesn't this case statement work?

Question

SELECT
case when PRODUCTS.PRODUCT_NAME in
select case when rank() over(order by ( sum(ag.RX_CNT) ) desc) < 6 then ( p.PRODUCT_NAME ) else 'XXXX' END RankedProduct
FROM
PAP_MONTHLYTIME_DIM m,
PAP_PRESCRIPTIONS_DEMOG_AGG ag,
PRODUCTS p,
PAP_ENROLLMENT_FLAGS_DIM f
WHERE
( m.MONTHLYTIME_DIM_ID = ag.MONTHLYTIME_DIM_ID )
AND ( ag.ENROLLMENT_FLAGS_DIM_ID = f.ENROLLMENT_FLAGS_DIM_ID )
AND ( p.PRODUCT_ID = ag.PRODUCT_DIM_ID )
AND ( f.ACTIVE_FLAG = 'Y' )
AND m.CALENDAR_YEAR_MONTH = '2007-04'
GROUP BY
m.MONTH_END_DATE,
p.PRODUCT_NAME
then
( PRODUCTS.PRODUCT_NAME ) else 'All Other' end as ProdNm,
PRODUCTS.PRODUCT_NAME,
sum(PAP_PRESCRIPTIONS_DEMOG_AGG.RX_CNT)
FROM
PRODUCTS,
PAP_PRESCRIPTIONS_DEMOG_AGG
WHERE
( PRODUCTS.PRODUCT_ID=PAP_PRESCRIPTIONS_DEMOG_AGG.PRODUCT_DIM_ID )
GROUP BY
PRODUCTS.PRODUCT_NAME
The first case statement is not working properly. First off - I know I can do this without the subquery in the case statement, but it's then tied to the Month and I don't want that.
The result set of the subquery contains valid product_names that match EXACTLY (I added LTRIM RTRIM just in case), but the ProdNm field still evaluates to "All Other" for them. If I change the subquery to something basic and remove the rank function, it works, but of course I need that function. My understanding is that it shouldn't matter what function is in the subquery. I thought Oracle would get the result set of the subquery first, then evaluate the case statement based on the result set (the subquery is obviously not correlated).
Any ideas?
Thanks.

Answer 1

My understanding is that it shouldn't matter what function is in the subquery. I thought Oracle would get the result set of the subquery first, then evaluate the case statement based on the result set (the subquery is obviously not correlated). It looks like the queries ARE somehow correlated. Consider the two simplified queries:
michaels>  SELECT   ename, deptno,
         CASE
            WHEN deptno IN (
                   SELECT CASE
                             WHEN ROW_NUMBER () OVER (ORDER BY NULL) < 3
                                THEN deptno
                             ELSE 1000
                          END
                     FROM dept)
               THEN 'Found'
            ELSE 'NOT Found'
         END FOUND
    FROM emp
ORDER BY deptno
ENAME          DEPTNO FOUND   
CLARK              10 NOT Found
KING               10 NOT Found
MILLER             10 NOT Found
JONES              20 NOT Found
FORD               20 NOT Found
ADAMS              20 NOT Found
SMITH              20 NOT Found
SCOTT              20 NOT Found
WARD               30 NOT Found
TURNER             30 NOT Found
ALLEN              30 NOT Found
JAMES              30 NOT Found
BLAKE              30 NOT Found
MARTIN             30 NOT Found
michaels>  SELECT   ename, deptno,
         CASE
            WHEN deptno IN (
                   SELECT *
                     FROM (SELECT CASE
                                     WHEN ROW_NUMBER () OVER (ORDER BY NULL) < 3
                                        THEN deptno
                                     ELSE 1000
                                  END
                             FROM dept))
               THEN 'Found'
            ELSE 'NOT Found'
         END FOUND
    FROM emp
ORDER BY deptno
ENAME          DEPTNO FOUND   
CLARK              10 Found   
KING               10 Found   
MILLER             10 Found   
JONES              20 Found   
FORD               20 Found   
ADAMS              20 Found   
SMITH              20 Found   
SCOTT              20 Found   
WARD               30 NOT Found
TURNER             30 NOT Found
ALLEN              30 NOT Found
JAMES              30 NOT Found
BLAKE              30 NOT Found
MARTIN             30 NOT FoundSo in the first query ROW_NUMBER() evaluates to NULL (not sure why) so the condition will never be satisfied! This is easily proofed when actually testing for nullity:
WHEN ROWNUM() OVER (ORDER BY NULL) IS NULL THEN
...will always show 'Found'!
Inlining the subquery »materializes« it, and ROW_NUMBER() gets the desired value.