Oracle 18c

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ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
CREATE TABLE table_name (id, cust_dt) AS
SELECT 1, TRUNC(SYSDATE, 'MM') - INTERVAL '1' MONTH  FROM DUAL UNION ALL
SELECT 2, TRUNC(SYSDATE, 'MM') - INTERVAL '1' DAY    FROM DUAL UNION ALL
SELECT 3, TRUNC(SYSDATE, 'MM') - INTERVAL '1' HOUR   FROM DUAL UNION ALL
SELECT 4, TRUNC(SYSDATE, 'MM') - INTERVAL '1' SECOND FROM DUAL UNION ALL
SELECT 4, TRUNC(SYSDATE, 'MM')                       FROM DUAL
5 rows affected

SELECT *
FROM   table_name
WHERE  TO_CHAR(cust_dt, 'MM-YYYY') = TO_CHAR(ADD_MONTHS(SYSDATE, -1), 'MM-YYYY')


ID
CUST_DT


1
2023-02-01 00:00:00

2
2023-02-28 00:00:00

3
2023-02-28 23:00:00

4
2023-02-28 23:59:59


SELECT *
FROM   table_name
WHERE  cust_dt BETWEEN TO_DATE('05-01-2022', 'mm-dd-yyyy')
                   AND TO_DATE('05-31-2022', 'mm-dd-yyyy')
SELECT *
FROM   table_name
WHERE  cust_dt >= ADD_MONTHS(TRUNC(SYSDATE, 'MM'), -1)
AND    cust_dt <  TRUNC(SYSDATE, 'MM')


ID
CUST_DT


1
2023-02-01 00:00:00

2
2023-02-28 00:00:00

3
2023-02-28 23:00:00

4
2023-02-28 23:59:59

ID	CUST_DT
1	2023-02-01 00:00:00
2	2023-02-28 00:00:00
3	2023-02-28 23:00:00
4	2023-02-28 23:59:59