Days count across the months with given start date and end date - snowflake-cloud-data-platform

Question

I have a snippet of a table as below :
Can somebody help me with the query that gives me report as below:

Answer 1

If you don't want to use a calendar dimension as Mike suggested (which is a good idea) the best option may be a user defined table function (UDTF). This UDTF does not depend on the DAYS_COUNT column. It calculates the days in each month and only requires a start and end date. It will generate as many rows as are required to fill the months in between.
select * from a, table(DAYS_IN_MONTHS(START_DATE, END_DATE));
create or replace function DAYS_IN_MONTHS(START_DATE date, END_DATE date)
returns table(MONTHS string, DAYS float)
language javascript
strict immutable
as
$$
{
initialize: function (argumentInfo, context) {},
processRow: function (row, rowWriter, context) {
let year = row.START_DATE.getFullYear();
let month = row.START_DATE.getMonth();
let endYear = row.END_DATE.getFullYear();
let endMonth = row.END_DATE.getMonth();
let isDone = year > endYear || (year == endYear && month > endMonth);
if (year == endYear && month == endMonth) {
rowWriter.writeRow({MONTHS: `${year}-${(""+(month+1)).padStart(2, '0')}`,DAYS: row.END_DATE.getDate() - row.START_DATE.getDate()});
isDone = true;
}
d = row.START_DATE
while (!isDone) {
if (year == endYear && month == endMonth) {
rowWriter.writeRow({MONTHS: `${year}-${(""+(month+1)).padStart(2, '0')}`,DAYS: row.END_DATE.getDate() - (d.getDate() - 1) });
isDone = true;
} else {
rowWriter.writeRow({MONTHS: `${year}-${(""+(month+1)).padStart(2, '0')}`,DAYS: new Date(year, month + 1, 0).getDate() - (d.getDate() - 1) });
month++;
if (month == 12) {
month = 0;
year++;
}
}
d = new Date(year, month, 1);
}
},
finalize: function (rowWriter, context) {},
}
$$;

Answer 2

It would be very helpful if you'd have a calendar dimension for something like this. As an example, you can create one with something like this:
CREATE TEMP TABLE calendar AS
SELECT dateadd(day,seq4(),'2017-01-01'::date) as cal_date,
date_trunc(month,cal_date) as cal_month_start,
dateadd(day,-1,(dateadd(month,1, cal_month_start))) as cal_month_end
FROM table(generator(rowcount => 10000));
With this calendar table, you can then join to it using the start and end dates and aggregate on that date to get the results. Using a CTE to replicate your data:
WITH x AS (
SELECT member_id, start_date, end_date
FROM (VALUES ('461043068_02','2018-08-07'::date,'2018-08-17'::date),
('461043068_01','2019-05-28'::date,'2019-06-28'::date)
) y (member_id, start_date, end_date)
)
Now, you can query x and join to calendar as such:
SELECT member_id, cal_month_start, count(*)
FROM x
JOIN calendar c
ON c.cal_date between dateadd(day,1,x.start_date) and x.end_date
GROUP BY 1,2;
This gives you the results you are looking for. Please note the need to add 1 to the start_date, so that you don't count the "edges" of your date ranges twice.
Also, I didn't format the cal_month_start in my query, but you can do that using a TO_VARCHAR() function, if needed.