Calculate first day and last day of week of current month - sqlite

Question

I want to calculate first date and last date of a week for the current month given current datetime.
For example, 01 December 2017 is first day and 02 December 2017 is last day of week for that week for the month of December. In the same week of year, 26 November 2017 is first day of week and
30 November 2017 is last day of week for previous month.
So if today is 01 December 2017, I should get 01-02 from current datetime , instead of 26-02 range.
PS: I am trying to do this thing in a query of Sqlite. I want to group some values on a weekly basis. The days of the week should belong to current month. Hence this requirement. Till now this is my query.
SELECT SUM(amount) as Y,
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '-'||strftime('%w', datetime(createdOn/1000, 'unixepoch'))||' day' )
||'-'||
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '+'||(6-strftime('%w', datetime(createdOn/1000, 'unixepoch')))||' day' ) AS X
FROM my_table
GROUP BY strftime('%d', datetime(createdOn/1000, 'unixepoch'), '-'||strftime('%w', datetime(createdOn/1000, 'unixepoch'))||' day' )
||'-'||
strftime('%d', datetime(createdOn/1000, 'unixepoch'), '+'||(6-strftime('%w', datetime(createdOn/1000, 'unixepoch')))||' day' )
How to achieve that; given current datetime.

Answer 1

Common table expressions are useful to hold intermediate results:
WITH t1 AS (
SELECT amount, date(createdOn / 1000, 'unixepoch', 'localtime') AS date
FROM my_table
),
t2 AS (
SELECT *,
date(date, 'weekday 6') AS end_of_week,
date(date, 'weekday 6', '-6 days') AS start_of_week
FROM t1
),
t3 AS (
SELECT *,
strftime('%m', date ) AS month,
strftime('%m', start_of_week) AS sowk_month,
strftime('%m', end_of_week ) AS eowk_month,
date(date, 'start of month') AS start_of_month,
date(date, '+1 month', 'start of month', '-1 day') AS end_of_month
FROM t2
),
t4 AS (
SELECT *,
CASE WHEN sowk_month = month THEN start_of_week
ELSE start_of_month
END AS week_in_month_start,
CASE WHEN eowk_month = month THEN end_of_week
ELSE end_of_month
END AS week_in_month_end
FROM t3
),
t5 AS (
SELECT amount,
week_in_month_start || '-' || week_in_month_end AS week_in_month
FROM t4
)
SELECT SUM(amount) AS Y,
week_in_month
FROM t5
GROUP BY week_in_month;