Combine two queries and add a new column - mysql

Question

DB-Fiddle
CREATE TABLE sales (
id int auto_increment primary key,
category VARCHAR(255),
event_date DATE,
sent_date DATE,
sales_Product_gross VARCHAR(255),
return_Product_gross VARCHAR(255)
);
INSERT INTO sales
(category, event_date, sent_date,
sales_Product_gross, return_Product_gross
)
VALUES
("CAT_01", "2017-05-30", "2017-05-30", "500", NULL),
("CAT_01", "2017-06-05", "2017-05-30", NULL, "250"),
("CAT_01", "2018-07-08", "2018-07-08", "700", NULL),
("CAT_01", "2018-07-18", "2018-07-08", NULL, "370"),
("CAT_01", "2019-02-15", "2019-02-15", "400", NULL),
("CAT_01", "2019-03-21", "2019-02-15", NULL, "120"),
("CAT_02", "2019-04-24", "2019-04-24", "300", NULL),
("CAT_02", "2019-04-30", "2019-04-24", NULL, "145"),
("CAT_02", "2019-12-14", "2019-12-14", "900", NULL),
("CAT_02", "2019-12-28", "2019-12-14", NULL, "340"),
("CAT_03", "2020-03-09", "2020-03-09", "800", NULL),
("CAT_03", "2020-03-17", "2020-03-09", NULL, "425");
The table displays the sales and returns in different categories.
Now, I want to calculate:
a) the return_rate per month per campaign and store it in a new column called calc_type with the name monthly.
b) the return_rate on a rolling 2 YEAR basis and also store it in the new column calc_type with the name rolling.
The result should look like this:
category calc_type year month return_rate
CAT_01 rolling NULL NULL 0.445
CAT_01 monthly 2017 5 0.500
CAT_01 monthly 2018 7 0.528
CAT_01 monthly 2019 2 0.300
CAT_02 rolling NULL NULL 0.404
CAT_02 monthly 2019 4 0.480
CAT_02 monthly 2019 12 0.377
CAT_03 rolling NULL NULL 0.531
CAT_03 monthly 2020 3 0.531
I have created a query for criteria a) and for criteria b). Separately, those queries work exactly the way I need it.
Now, I tried to combine them using UNION ALL the same way it is done here:
SELECT
category,
'rolling' AS calc_type,
'NULL' AS year,
'NULL' As month,
sum(return_Product_gross) / sum(sales_Product_gross) as return_rate
FROM sales
WHERE sent_date BETWEEN DATE_SUB(CURDATE(), INTERVAL 2 YEAR) AND CURDATE()
GROUP BY 1,2,3,4
ORDER BY 1,2,3,4;
UNION ALL
SELECT
category,
'monthly' AS calc_type,
YEAR(sent_date) AS year,
MONTH(sent_date) AS month,
sum(return_Product_gross) / sum(sales_Product_gross) as return_rate
FROM sales
WHERE sent_date BETWEEN "2017-01-01" AND CURDATE()
GROUP BY 1,2,3,4
ORDER BY 1,2,3,4;
However, now only the values for rolling are displayed in the result.
What do I need to change in my queries to get the expected result?

Answer 1

This query looks worked:
SELECT
category,
'rolling' AS calc_type,
'NULL' AS year,
'NULL' As month,
sum(return_Product_gross) / sum(sales_Product_gross) as return_rate
FROM sales
WHERE sent_date BETWEEN DATE_SUB(CURDATE(), INTERVAL 2 YEAR) AND CURDATE()
GROUP BY category, year, month
UNION ALL
SELECT
category,
'monthly' AS calc_type,
YEAR(sent_date) AS year,
MONTH(sent_date) AS month,
sum(return_Product_gross) / sum(sales_Product_gross) as return_rate
FROM sales
WHERE sent_date BETWEEN "2017-01-01" AND CURDATE()
GROUP BY category, year, month
ORDER BY category, calc_type DESC, year, month;
DBFiddle