Latest record with active flag 'Y' (if only N, select that record)

Question

Hi All,
I am having some records in table emp and need to select one record per id, which meets following criteria:-
(1) if there is only one record for given id, select them. eg- '0154', '0155'
(2) if more than one record then
(2a) select record with active_flag = 'Y'.
(2b) if more than one record with flag 'Y', select latest record where flag = 'Y'. Max eff_date.
Emp table:-
with emp as (
select '0066' id, 'ABC' name, 'Y' active_flag, to_date('01-01-2009', 'dd-mm-yyyy') eff_date  from dual union
select '0066', 'PQR', 'N', to_date('01-01-2010', 'dd-mm-yyyy') from dual union
select '0066', 'XYZ', 'N', to_date('01-03-2010', 'dd-mm-yyyy') from dual union
select '0154', 'PQR', 'N', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
select '0155', 'DEF', 'Y', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
select '8686', 'THY', 'N', to_date('01-10-2010', 'dd-mm-yyyy') from dual union
select '8686', 'QWE', 'N', to_date('01-01-2010', 'dd-mm-yyyy') from dual union
select '8686', 'POI', 'Y', to_date('01-04-2010', 'dd-mm-yyyy') from dual union
select '8686', 'MNB', 'Y', to_date('01-03-2010', 'dd-mm-yyyy') from dual
select * from emp;
Output records:-
with emp_selected as (
select '0066' id, 'ABC' name, 'Y' active_flag, to_date('01-01-2009', 'dd-mm-yyyy') eff_date  from dual union
select '0154', 'PQR', 'N', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
select '0155', 'DEF', 'Y', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
select '8686', 'POI', 'Y', to_date('01-04-2010', 'dd-mm-yyyy') from dual
select * from emp_selected;Request you to please look at it.
Regards,
Ritesh

Answer 1

Thanks for posting the sample data and expected resutls in such a useful way. It makes life so much easier.
Assuming that the only valid values in active_flag are Y and N, and that there are no nulls, then this is one way:
SQL > with emp as (
  2   select '0066' id, 'ABC' name, 'Y' active_flag, to_date('01-01-2009', 'dd-mm-yyyy') eff_date  from dual union
  3   select '0066', 'PQR', 'N', to_date('01-01-2010', 'dd-mm-yyyy') from dual union
  4   select '0066', 'XYZ', 'N', to_date('01-03-2010', 'dd-mm-yyyy') from dual union
  5   select '0154', 'PQR', 'N', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
  6   select '0155', 'DEF', 'Y', to_date('01-05-2010', 'dd-mm-yyyy') from dual union
  7   select '8686', 'THY', 'N', to_date('01-10-2010', 'dd-mm-yyyy') from dual union
  8   select '8686', 'QWE', 'N', to_date('01-01-2010', 'dd-mm-yyyy') from dual union
  9   select '8686', 'POI', 'Y', to_date('01-04-2010', 'dd-mm-yyyy') from dual union
10   select '8686', 'MNB', 'Y', to_date('01-03-2010', 'dd-mm-yyyy') from dual)
11   SELECT id, name, active_flag, eff_date
12   FROM (SELECT id, name, active_flag, eff_date,
13                ROW_NUMBER() OVER(PARTITION BY id
14                                  ORDER BY active_flag desc, eff_date desc) rn
15         FROM emp)
16   WHERE rn = 1;
ID   NAM A EFF_DATE
0066 ABC Y 01-JAN-09
0154 PQR N 01-MAY-10
0155 DEF Y 01-MAY-10
8686 POI Y 01-APR-10If there could be nulls in active_flag, then you could use NVL to set the value to Y or N in the order by to sort it "correctly" based on your requirements.
If there could be values other than Y and N, then use a case statement in the order by to fix the order to give preference to what you want.
For example, if valid values could be Y, N, P and you wanted them selected in that order, then neither ascending nor descending sorts would be right, so you could do something like:
ORDER BY CASE active_flag WHEN 'Y' THEN 1
                          WHEN 'N' THEN 2
                          WHEN 'P' THEN 3
                          ELSE 4 ENDJohn