SQL - How to append a period - sqlite

Question

I have an existing SQLite_table like this:
startdate - enddate
2018-01-01 - 2018-06-30
2018-07-01 - 2018-12-31
2019-01-01 - 2019-06-30
2019-07-01 - 2019-12-31
2020-01-01 - 2020-06-30
2020-07-01 - 2020-12-31
2021-01-01 - 2021-06-30
What is the SQL-Statement for the result;
The result should be:
2019-11-01 2020-12-31 // 60 Days difference
2020-01-01 2020-06-30 // 180 Days difference
2020-07-01 2020-12-31 // 180 Days difference
2021-01-01 2021-06-30 // 180 Days difference
'2019-11-01' is entered via the search field in my Android app as input
The point is the output of the small period at the beginning / the
insertion of the first period in the statement
I tried 'Union' and it gives me an error.
How can I do this with a query ?
I am thankful for any help
and what is the SQL statement, when it should
return data from '2019-11-01' until 'now'
2019-11-01 2020-12-31 // 60 Days difference
2020-01-01 2020-06-30 // 180 Days difference
2020-07-01 2020-12-31 // 180 Days difference
2021-01-01 2021-02-16 // 46 Days difference ! !
Thank's

Answer 1

You need all the rows where enddate is less or equal than '2019-11-01':
SELECT MAX(startdate, '2019-11-01') startdate, enddate
FROM tablename
WHERE enddate >= '2019-11-01'
See the demo.
Results:
startdate
enddate
2019-11-01
2019-12-31
2020-01-01
2020-06-30
2020-07-01
2020-12-31
2021-01-01
2021-06-30
Edit, for your 2nd question:
SELECT MAX(startdate, '2019-11-01') startdate,
MIN(enddate, CURRENT_DATE) enddate
FROM tablename
WHERE enddate >= '2019-11-01' AND startdate <= CURRENT_DATE
See the demo.
Results:
startdate
enddate
2019-11-01
2019-12-31
2020-01-01
2020-06-30
2020-07-01
2020-12-31
2021-01-01
2021-02-16