SQL query to aggregate data based on months (Postgres) - postgresql

Question

The table that I querying is :
table testing_table:
testType | period_from | period_to| copies |
1 | 20180101| 20181201| 1|
2 | 20180101 | 20191201| 1|
3 | 20190101| 20191201| 1|
I want to loop through the array and use the below query to generate values like this:
DateVar | ABTEST | CDTEST | EFTEST |
20180101| 4| 0| 0|
20180201| 3| 4| 2|
dateVar = ['20180101','20180201','20180501'].
I am trying to develop an sql query like this:
SELECT
SUM (
CASE
WHEN (testType = 1 AND (period_from <= dateVar AND period_to >= dateVar)) THEN
copies
ELSE
0
END
) AS "ABTEST",
SUM (
CASE
WHEN (testType = 2 AND (period_from <= dateVar AND period_to >= dateVar)) THEN
copies
ELSE
0
END
) AS "CDTEST",
SUM (
CASE
WHEN (testType = 3 AND (period_from <= dateVar AND period_to >= dateVar)) THEN
copies
ELSE
0
END
) AS "EFTEST"
FROM
testing_table;
I am lost as to what to do with it. Do I look into functions?

Answer 1

I think you should use unnest function to accomplish what you are asking i have written a query you may want to check
SELECT DTVAR,
SUM(CASE
WHEN TestType = 1
THEN copies
ELSE 0
END) AS 'ABTEST',
SUM(CASE
WHEN TestType = 2
THEN copies
ELSE 0
END) AS 'CDTEST',
SUM(CASE
WHEN TestType = 3
THEN copies
ELSE 0
END) AS 'EFTEST'
FROM (
SELECT DTVAR, TestType, sum(copies) AS copies
FROM testing_table
INNER JOIN (
SELECT DTVAR
FROM unnest(dateVar ['20180101','20180201','20180501']) AS DTVAR
) AA
ON (
period_from <= DTVAR
AND period_to >= DTVAR
)
GROUP BY DTVAR, TestType
) A
GROUP BY DTVAR
hope this helps..