Oracle 18c

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CREATE TABLE purchase ( purchasedate ) AS
SELECT DATE '2019-01-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 5 UNION ALL
SELECT DATE '2019-02-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 3 UNION ALL
SELECT DATE '2020-01-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 3 UNION ALL
SELECT DATE '2020-02-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 2 UNION ALL
SELECT DATE '2020-03-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 4 UNION ALL
SELECT DATE '2020-04-01' + LEVEL - 1 FROM DUAL CONNECT BY LEVEL <= 1;
18 rows affected

ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
SELECT TO_CHAR(PURCHASEDATE, 'MM YYYY') AS monthyear,
       COUNT(*) AS frequency
FROM   PURCHASE
GROUP BY
       TO_CHAR(PURCHASEDATE, 'MM YYYY');


MONTHYEAR
FREQUENCY


03 2020
4

01 2019
5

01 2020
3

02 2020
2

02 2019
3

04 2020
1


SELECT TRUNC(PURCHASEDATE,'MM') AS monthyear,
       COUNT(*) AS frequency
FROM   PURCHASE
GROUP BY
       TRUNC(PURCHASEDATE,'MM');


MONTHYEAR
FREQUENCY


2020-03-01 00:00:00
4

2020-04-01 00:00:00
1

2020-02-01 00:00:00
2

2020-01-01 00:00:00
3

2019-01-01 00:00:00
5

2019-02-01 00:00:00
3


SELECT EXTRACT( YEAR FROM PURCHASEDATE) AS year,
       EXTRACT( MONTH FROM PURCHASEDATE) AS month,
       COUNT(*) AS frequency
FROM   PURCHASE
GROUP BY
       EXTRACT( YEAR FROM PURCHASEDATE),
       EXTRACT( MONTH FROM PURCHASEDATE);


YEAR
MONTH
FREQUENCY


2019
1
5

2020
1
3

2020
2
2

2020
4
1

2019
2
3

2020
3
4

MONTHYEAR	FREQUENCY
2020-03-01 00:00:00	4
2020-04-01 00:00:00	1
2020-02-01 00:00:00	2
2020-01-01 00:00:00	3
2019-01-01 00:00:00	5
2019-02-01 00:00:00	3