SQL - Query for a meeting room - mysql

Question

I need a help to create a query to return if the period selected already has a meeting in the room.
I have table rep_reuniao with the following design
ID --> int
ROOM --> int
DATE_BEGIN --> DATETIME
DATE_END --> DATETIME
Now an insert of a row in the table rep_reuniao looks like this
ID --> 1
ROOM --> 2
DATE_BEGIN --> 2014-02-21 17:00:00
DATE_END --> 2014-02-21 18:00:00
I will create an Jquery Ajax script to return a true or false JSON response based on the selected datetime.
So the query will have the ROOM, DATE_BEGIN in this format 2014-02-21 17:00 and DATE_END in the same format 2014-02-21 18:00
I Have checked another responses, but the most of them is a query to show the Rooms available. In my desing, a room is always available, except when exist a register in the table.
Example 1
ROOM 1 is already in use from 2014-02-21 17:00:00 to 2014-02-21 18:00:00
Need create a query to return a value (Anything) if the user select a room in:
BEGIN = 2012-02-21 16:30:00
END = 2012-02-21 17:30:00
See? The room in use in the table begins 17:00 so today my query easly return a value if the begin selected by the user is the same. But the End date selected by the user is between the time already in use.
Well, the selected time by the user cannot be in use lookin into the begin date and end date. I have no ideas right now, anyone can help me?
You need to check if one date range overlaps another date range.
New Date Range = |-----------|
Test1 = |=====|
Test2 = |=====|
Test3 = |=====|
Test4 = |=====|
Test5 = |=====|
Test6 = |=================|
Only Test1 and Test5 do not overlap.
Sorry if has any English errors. If someone are able to fix, I'll appreciate.

Answer 1

The correct logic over overlapping timeframes is that two time frames overlap when both these conditions are true:
the first starts before the other ends
the first ends after the other starts
In SQL, these can be expressed easily:
SELECT r.*
FROM rep_reuniao r
WHERE #UserBegin <= r.DATE_END AND
#UserEnd >= r.DATE_BEGIN;
Note that this can return multiple rows, when multiple meetings occur during the specified timeframe.
If you want true/false or 0/1, then use aggregation and case:
SELECT (case when count(*) = 0 then 'false' else 'true' end) as HasOverlappingRooms
FROM rep_reuniao r
WHERE #UserBegin <= r.DATE_END AND
#UserEnd >= r.DATE_BEGIN;

Answer 2

Try this, if the query returns any rows that means the room is already booked.
A simple explanation is the user gives #UserBegin and #UserEnd time that they need the room for.
And if the #UserBegin is between a row's begin and end then it is already booked.
Similarly, if the #UserEnd is between a row's begin and end, even then the room is booked.
SELECT *
FROM rep_reuniao r
WHERE (#UserBegin BETWEEN r.DATE_BEGIN AND r.DATE_END)
OR (#UserEnd BETWEEN r.DATE_BEGIN AND r.DATE_END)
OR (#UserBegin <= r.DATE_BEGIN AND #UserEnd >= r.DATE_END)
From here you can extend this to return a bool like shown
SELECT CASE WHEN EXISTS ( /* The above query */ ) THEN 0 ELSE 1
This should return 1 or 0, when the room is available or not respectively.

Answer 3

You could try the following query. It should catch when a date in the table falls within your range, or when you range falls within a date in the table:
SELECT CASE WHEN COUNT(*) > 1 THEN 1 ELSE 0 END AS AlreadyBooked
FROM rep_reuniao r
WHERE (#UserBegin BETWEEN r.DATE_BEGIN AND r.DATE_END)
OR (r.DATE_BEGIN BETWEEN #UserBegin AND #UserEnd)
The query checks for any rows where either #UserBegin falls within the range in the row or where the row's start date falls withing #userBegin - #UserEnd. It will find cases where the ranges partially overlap, or where either range falls within the other.