Conditional Grouping in Oracle SQL

Question

I want to group the below table by country and if the country is blank then I want to group by state. Is there a way to do in plain SQL? I am able to group if there is no condition on state!!

+--------+-------+---------+
| EMP ID | STATE | COUNTRY |
+--------+-------+---------+
|      1 | AP    | IN      |
|      2 | UP    | IN      |
|      3 | MP    | IN      |
|      4 | NJ    | US      |
|      5 | NY    | US      |
|      6 | CA    | US      |
|      7 | PA    |         |
|      8 | PA    |         |
|      9 | CR    |         |
+--------+-------+---------+

Expected Output:

+--------+-----------+---------+
| EMP ID |   STATE   | COUNTRY |
+--------+-----------+---------+
| 1,2,3  | AP,UP, MP | IN      |
| 4,5,6  | NJ,NY,CA  | US      |
| 7,8    | PA,PA     |         |
| 9      | CR        |         |
+--------+-----------+---------+

Answer 1

Do this:

WITH d AS (
SELECT 1 id, 'AP' state, 'IN' country FROM DUAL UNION ALL
SELECT 2 id, 'UP' state, 'IN' country FROM DUAL UNION ALL
SELECT 3 id, 'MP' state, 'IN' country FROM DUAL UNION ALL
SELECT 4 id, 'NJ' state, 'US' country FROM DUAL UNION ALL
SELECT 5 id, 'NY' state, 'US' country FROM DUAL UNION ALL
SELECT 6 id, 'CA' state, 'US' country FROM DUAL UNION ALL
SELECT 7 id, 'PA' state, null country FROM DUAL UNION ALL
SELECT 8 id, 'PA' state, null country FROM DUAL UNION ALL
SELECT 9 id, 'CR' state, null country FROM DUAL)
SELECT listagg(id,',') within group ( order by id),
       listagg(state,',') within group (order by state),
       country 
       FROM d
       group by nvl(country, state), country
       order by 1

Answer 2

Use a case statement in your SELECT:

SELECT EMP_ID, STATE, CASE WHEN COUNTRY IS NULL THEN STATE ELSE COUNTRY END AS COUNTRY_STATE
FROM [TABLE]

Then you can use LISTAGG() to rollup the values, depending on your version of Oracle

SELECT LISTAGG(EMP_ID, ',') WITHIN GROUP,
    LISTAGG(STATE, ',') WITHIN GROUP,
    COUNTRY_STATE
FROM (
SELECT EMP_ID, STATE, CASE WHEN COUNTRY IS NULL THEN STATE ELSE COUNTRY        END AS COUNTRY_STATE
FROM [TABLE] )
GROUP BY COUNTRY_STATE