How to calculate values from previous month to current month - postgresql

Question

I want to calculate this table. Everytime that there is a new participant per month it will add the previous value to current value.
month
no_participant
2021-01
10
2021-02
20
2021-03
5
2021-04
17
Something like this, output
month
no_participant
count
2021-01
10
10
2021-02
20
30
2021-03
5
35
2021-04
17
52
Here's my query: I am using Postgres. Thanks to your help
SELECT (TO_CHAR(CSD.SCHEDULED_START_DATETIME, 'YYYY-MM'))AS MONTH,
COUNT(DISTINCT PARTICIPANT_ID) AS PARTICIPANT
FROM TSUP.COURSE_SCHEDULE_DETAIL AS CSD
INNER JOIN TSUP.COURSE_PARTICIPANT AS CP
ON CSD.COURSE_SCHEDULE_ID = CP.COURSE_SCHEDULE_ID
INNER JOIN(
SELECT
MIN(COALESCE(CSD.RESCHEDULED_START_DATETIME, CSD.SCHEDULED_START_DATETIME)) AS SCHEDULED_START_DATETIME,
MAX(COALESCE(CSD.RESCHEDULED_END_DATETIME, CSD.SCHEDULED_END_DATETIME)) AS SCHEDULED_END_DATETIME,
COUNT(CSD.SCHEDULED_START_DATETIME) AS "COUNT"
FROM TSUP.COURSE_SCHEDULE_DETAIL AS CSD
INNER JOIN (
SELECT CP.PARTICIPANT_ID AS "PARTICIPANT",
MIN(COALESCE(CSD.RESCHEDULED_START_DATETIME, CSD.SCHEDULED_START_DATETIME)) AS SCHEDULED_START_DATETIME,
MAX(COALESCE(CSD.RESCHEDULED_END_DATETIME, CSD.SCHEDULED_END_DATETIME)) AS SCHEDULED_END_DATETIME
FROM TSUP.COURSE_PARTICIPANT AS CP
INNER JOIN TSUP.COURSE_SCHEDULE_DETAIL AS CSD
ON CP.COURSE_SCHEDULE_ID = CSD.COURSE_SCHEDULE_ID
INNER JOIN TSUP.COURSE_SCHEDULE AS CS
ON CSD.ID = CS.ID
INNER JOIN TSUP.COURSE AS C
ON CS.COURSE_ID = C.ID
INNER JOIN TSUP.COURSE_CATEGORY AS CC
ON C.COURSE_CATEGORY_ID = CC.ID
INNER JOIN TSUP.EMPLOYEE AS E
ON CP.PARTICIPANT_ID = E.ID
INNER JOIN TSUP.MEMBER_ROLE AS MR
ON E.MEMBER_ROLE_ID = MR.ID
WHERE C.MANDATORY = 'Yes'
AND MR.ROLE_TYPE = 'Dev'
AND CC.CATEGORY = 'JJ'
GROUP BY CP.PARTICIPANT_ID)
TEMP ON CSD.SCHEDULED_START_DATETIME = TEMP.SCHEDULED_START_DATETIME
GROUP BY CSD.RESCHEDULED_START_DATETIME, CSD.SCHEDULED_START_DATETIME,
CSD.RESCHEDULED_END_DATETIME, CSD.SCHEDULED_END_DATETIME
)
TEMP ON CSD.SCHEDULED_START_DATETIME = TEMP.SCHEDULED_START_DATETIME
GROUP BY MONTH

Answer 1

The query you provided is verbose, and also does not seem to exactly line up with the sample data. I will give the following query based on the sample data shown:
SELECT month, no_participant, SUM(no_participant) OVER (ORDER BY month) AS count
FROM yourTable
ORDER BY month;
The above logic uses SUM() as an analytic function.