Oracle 21c

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CREATE TABLE employees (job_id, salary) AS
SELECT 1, 100 FROM DUAL CONNECT BY LEVEL <= 10 UNION ALL
SELECT 2, 200 FROM DUAL CONNECT BY LEVEL <= 10 UNION ALL
SELECT 3,  10 FROM DUAL CONNECT BY LEVEL <=  9 UNION ALL
SELECT 3, 200 FROM DUAL;
30 rows affected

SELECT job_id,
       MIN(AVG(salary))
FROM   employees
GROUP BY job_id
ORA-00937: not a single-group group function

SELECT job_id,
       MIN(avg_sal)
FROM   (
  SELECT job_id,
         AVG(salary) AS avg_sal
  FROM   employees
  GROUP BY job_id
)
ORA-00937: not a single-group group function

SELECT MIN(job_id) KEEP (DENSE_RANK FIRST ORDER BY avg_sal),
       MIN(avg_sal)
FROM   (
  SELECT job_id,
         AVG(salary) AS avg_sal
  FROM   employees
  GROUP BY job_id
)


MIN(JOB_ID)KEEP(DENSE_RANKFIRSTORDERBYAVG_SAL)
MIN(AVG_SAL)


3
29


SELECT MIN(MIN(job_id)) KEEP (DENSE_RANK FIRST ORDER BY AVG(salary)) AS job_id,
       MIN(AVG(salary))
FROM   employees
GROUP BY job_id


JOB_ID
MIN(AVG(SALARY))


3
29


SELECT job_id, AVG(salary)
FROM employees
GROUP BY job_id
HAVING AVG(salary) = (SELECT MIN(AVG(salary))
                      FROM employees
                      GROUP BY job_id); 


JOB_ID
AVG(SALARY)


3
29


SELECT job_id, AVG(salary)
FROM employees
GROUP BY job_id
ORDER BY AVG(salary)
FETCH FIRST ROW ONLY; 


JOB_ID
AVG(SALARY)


3
29


SELECT *
FROM   (
  SELECT job_id, AVG(salary)
  FROM employees
  GROUP BY job_id
  ORDER BY AVG(salary)
)
WHERE ROWNUM = 1;


JOB_ID
AVG(SALARY)


3
29