Find date scope from MySQL efficiently - mysql

Question

Here is my DiscountPeriod table's structure:
id
room_id
date_from
date_last
discount
Imagine that we have discount starting 01 December 2017 and ending in in 10 December 2017.
I'm searching for date-range to see if it has discount.
So date range might be totally or partly inside some of discount periods. 3 example date-ranges for search:
From 02 December to 10 December (fully inside one of discount periods)
From 20 November to 4 December (partly inside)
From 5 December to 15 December (partly inside)
Expected for all of 3 examples above is to get discount that starts in 01 December 2017 and ends in 10 December 2017.
Currently my query takes only those results which is completely inside exact period from database.
It looks like this:
SELECT * FROM `DiscountPeriod` WHERE (`room_id`=1517) AND (`date_last` >= '2017-12-12') AND (`date_from` <= '2017-12-20');
Question is, how to fit all of 3 possible search cases into 1 query for efficient searching in MySQL database tables?
Expected result is
All of following scopes: From 02 Dec to 10 Dec, From 20 Nov to 4 Dec, From 5 Dec to 15 Dec should return back 1-10 december discount.

Answer 1

This looks like an overlapping range problem. If you want to return all discounts which overlap with 1-10 December 2017, then try the following query:
SELECT *
FROM DiscountPeriod
WHERE
room_id = 1517 AND
'2017-12-01' <= date_last AND '2017-12-10' >= date_from;
Here is a demo which uses your test data. All three discount ranges you suggested show up in the result set. But a range lying completely outside 1-10 December 2017 is absent, as we would expect.
Demo