Expected column value is not selecting

Question

Hi All,
I have to table like below records
Select * from pa_tbl where emplid=’5705838’
Gives the Below result.
EMPLID    COMPANY     EFFDT_CODE        STATE    RESIDENT
5705838    T01         8/20/1998        CO            N          
5705838    T01         8/20/1998        PA            Y      
5705838    T01         1/1/2001        CO            N      
5705838    T01         1/1/2001        PA            Y  
From above result I have to select  only ‘state_code’  
1.Condition is  resident is ‘N’ with max(effdt)
2nd condition select state_code in ‘AK’, ‘NV’, ‘CO’, ‘PR’ among lot of state_codes .
Above example that i have given only for 'CO' state_code
I am able to extract sate code like  ’CO’ using below query
SELECT  STATE
FROM PS pa_tbl S
WHERE S.EMPLID  ='5705838'
AND S.RESIDENT = 'N'
AND S.STATE IN('AK','NV','CO','MI')
AND S.EFFDT   = (SELECT MAX(EFFDT)
                    FROM PS pa_tbl
                    WHERE EMPLID  = S.EMPLID
                    AND COMPANY = S.COMPANY
                    AND EFFDT <=SYSDATE);
Problem:-
Here user entered effdt is 1/1/2001 with state_code is 'PA' and resident='Y 'which is latest record. In this case my query should return NULL/NODATA found.
But my query returns STATE_CODE=CO (this is wrong)
How to write a sql query can any body give me advice please?
Thanks,
Krupa

Answer 1

Use analytic ROW_NUMBER:
SCOTT@orcl > select  *
  2    from  tbl
  3  /
    EMPLID COM EFFDT     ST R
   5705838 T01 20-AUG-98 CO N
   5705838 T01 20-AUG-98 PA Y
   5705838 T01 01-JAN-01 CO N
   5705838 T01 01-JAN-01 PA Y
SCOTT@orcl > with t as (
  2             select  state,
  3                     row_number() over(order by effdt desc) rn
  4               from  tbl
  5               where emplid = 5705838
  6                 and resident = 'N'
  7                 and state in ('AK','NV','CO','MI')
  8            )
  9  select  state
10    from  t
11    where rn = 1
12  /
ST
CO
SCOTT@orcl > with t as (
  2             select  state,
  3                     row_number() over(order by effdt desc) rn
  4               from  tbl
  5               where emplid = 5705838
  6                 and resident = 'Y'
  7                 and state in ('AK','NV','CO','MI')
  8            )
  9  select  state
10    from  t
11    where rn = 1
12  /
no rows selected
SCOTT@orcl >
SY.