How to group by month and year? - sql

Question

I have a table PURCHASE with a date column PURCHASEDATE which is in DATE format. I'm trying to get the purchases grouped by month and year. To do so, I try with:
SELECT
TO_CHAR(PURCHASEDATE, 'MM YYYY') AS MONTHYEAR
FROM PURCHASE
GROUP BY TO_CHAR(PURCHASEDATE, 'MM YYYY');
I have also tryied with GROUP BY EXTRACT(MONTH FROM PURCHASEDATE), EXTRACT(YEAR FROM PURCHASEDATE) but neither worked.
I'm rusty with SQL querys :S.
EDIT
Table cloumns
Thanks ahead!

Answer 1

If you have the sample data:
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;
Then, you can use your query:
SELECT TO_CHAR(PURCHASEDATE, 'MM YYYY') AS monthyear,
COUNT(*) AS frequency
FROM PURCHASE
GROUP BY
TO_CHAR(PURCHASEDATE, 'MM YYYY');
Which outputs:
MONTHYEAR | FREQUENCY
:-------- | --------:
03 2020 | 4
01 2019 | 5
01 2020 | 3
02 2020 | 2
02 2019 | 3
04 2020 | 1
Or, you can use TRUNC:
SELECT TRUNC(PURCHASEDATE,'MM') AS monthyear,
COUNT(*) AS frequency
FROM PURCHASE
GROUP BY
TRUNC(PURCHASEDATE,'MM');
Which outputs:
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
Or, you can use EXTRACT:
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);
Which outputs:
YEAR | MONTH | FREQUENCY
---: | ----: | --------:
2019 | 1 | 5
2020 | 1 | 3
2020 | 2 | 2
2020 | 4 | 1
2019 | 2 | 3
2020 | 3 | 4
db<>fiddle here

Answer 2

Is this what you want?
SELECT
TO_CHAR(PURCHASEDATE, 'MM YYYY') AS MONTHYEAR,
SUM(TOTAL) AS TOTAL
FROM PURCHASE
GROUP BY
TO_CHAR(PURCHASEDATE, 'MM YYYY');