Oracle 11g Release 2

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CREATE TABLE tableA ( class_time ) AS
SELECT DATE '2019-12-16' + INTERVAL '02:00' HOUR TO MINUTE FROM DUAL UNION ALL
SELECT DATE '2019-12-16' + INTERVAL '02:30' HOUR TO MINUTE FROM DUAL UNION ALL
SELECT DATE '2019-12-16' + INTERVAL '03:00' HOUR TO MINUTE FROM DUAL UNION ALL
SELECT DATE '2019-12-16' + INTERVAL '03:30' HOUR TO MINUTE FROM DUAL UNION ALL
SELECT DATE '2019-12-16' + INTERVAL '04:00' HOUR TO MINUTE FROM DUAL
5 rows affected

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
SELECT class_time from tableA
UNION ALL
SELECT MAX( class_time ) + INTERVAL '30' MINUTE FROM tableA


CLASS_TIME


2019-12-16 02:00:00

2019-12-16 02:30:00

2019-12-16 03:00:00

2019-12-16 03:30:00

2019-12-16 04:00:00

2019-12-16 04:30:00


SELECT class_time from tableA
UNION ALL
SELECT MAX( class_time ) + 30 / ( 24 /* hours */ * 60 /* minutes */ )  FROM tableA


CLASS_TIME


2019-12-16 02:00:00

2019-12-16 02:30:00

2019-12-16 03:00:00

2019-12-16 03:30:00

2019-12-16 04:00:00

2019-12-16 04:30:00


CREATE TABLE tableB ( class_time ) AS
SELECT '02:00 AM' FROM DUAL UNION ALL
SELECT '02:30 AM' FROM DUAL UNION ALL
SELECT '03:00 AM' FROM DUAL UNION ALL
SELECT '03:30 AM' FROM DUAL UNION ALL
SELECT '04:00 AM' FROM DUAL;
5 rows affected

SELECT class_time from tableB
UNION ALL
SELECT TO_CHAR(
         MAX( TO_DATE( class_time, 'HH12:MI AM' ) )
         + INTERVAL '30' MINUTE,
         'HH12:MI AM'
       )
FROM   tableB


CLASS_TIME


02:00 AM

02:30 AM

03:00 AM

03:30 AM

04:00 AM

04:30 AM