Вы можете использовать следующее:
Я создал таблицу и данные в соответствии с примером.
-- Preparing the data
CREATE TABLE EMPLOYEES (
EMP NUMBER,
DATE1 DATE,
DEPT VARCHAR2(100)
);
INSERT INTO EMPLOYEES VALUES (
1,
TO_DATE('01/21', 'MM/DD'),
'Abc'
);
INSERT INTO EMPLOYEES VALUES (
1,
TO_DATE('02/15', 'MM/DD'),
'Xyz'
);
INSERT INTO EMPLOYEES VALUES (
1,
TO_DATE('10/19', 'MM/DD'),
'Cba'
);
INSERT INTO EMPLOYEES VALUES (
2,
TO_DATE('01/21', 'MM/DD'),
'Abc'
);
INSERT INTO EMPLOYEES VALUES (
2,
TO_DATE('02/15', 'MM/DD'),
'Xyz'
);
INSERT INTO EMPLOYEES VALUES (
2,
TO_DATE('04', 'MM'),
'Uvw'
);
-
-- Final data in the table
SELECT
*
FROM
EMPLOYEES;

-- Your Query
SELECT
EMP,
DEPT
FROM
(
SELECT
EMP,
DEPT,
ROW_NUMBER() OVER(
PARTITION BY EMP
ORDER BY
DURATION DESC NULLS LAST
) AS RN
FROM
(
SELECT
EMP,
DATE1,
DEPT,
MONTHS_BETWEEN(LEAD(DATE1, 1) OVER(
PARTITION BY EMP
ORDER BY
DATE1
), DATE1) AS DURATION
FROM
EMPLOYEES
)
WHERE
DURATION >= 6
OR DURATION IS NULL
)
WHERE
RN = 1;
Выход:

Надеюсь, это будет вам полезно.
Ура !!