Question

I’ve got two tables called hotels and hotel locations. In the hotels table I have HotelId, hotelName. In the hotelLocations table I have HotelId, HotelNorthing, HotelEasting. HotelId is a foreign key that references HotelId in the hotels table, HotelNorthing and HotelEasting are UTM co-ordinates that hold the northing and easting values for the hotels.

I would like to find, using this data the 2 hotels that are closest to each other and display with a query the hotel name and id from the hotels table and the distance from the calculation. I previously tried all sorts of cross joins but came up short. I used the Pythagoras theorem to calculate the distance between the hotels but the structure of an appropriate query has eluded me.

Answer 1

Assuming MS SQL 2008 or later I’d use the built in geography type:

insert into locations (name, location) values
('Hotel1', 'Point(138.58 -34.92)'),
('Hotel2', 'POINT(138.97 -34.78)'),
('Hotel3', 'POINT(138.00 -34.00)'),
('Hotel4', 'POINT(138.57 -34.01)'),
('Hotel5', 'POINT(138.50 -34.03)'),
('Hotel6', 'POINT(138.49 -34.04)'),
('Hotel7', 'POINT(138.88 -34.04)')


declare @StartLocation geography
select @StartLocation = location
from Locations 
where name = 'Hotel1'

select location.STDistance(@StartLocation)
from locations

This will give you the distance from Hotel1 to all the other hotel’s, then it’s just a matter of sorting the list and taking the top 2.

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EDIT: To calculate from every hotel to every other hotel:

create table locations
(
    ID INT IDENTITY(1,1),
    Name varchar(50),
    Location geography
)

insert into locations (name, location) values
('Hotel1', 'Point(138.58 -34.92)'),
('Hotel2', 'POINT(138.59 -34.93)'),
('Hotel3', 'POINT(138.00 -34.00)'),
('Hotel4', 'POINT(138.57 -34.01)'),
('Hotel5', 'POINT(138.50 -34.03)'),
('Hotel6', 'POINT(138.49 -34.04)'),
('Hotel7', 'POINT(138.88 -34.04)')

select l1.name, l2.name, l1.location.STDistance(l2.Location)
FROM Locations l1
JOIN Locations l2 on l2.ID < l1.ID

---

EDIT 2:
Split Hotel Names out into seperate table:

create table locationNames
(
    ID INT IDENTITY(1,1),
    Name VARCHAR(50)
)
insert into locationNames (Name) VALUES
('Hotel1'),
('Hotel2'),
('Hotel3'),
('Hotel4'),
('Hotel5'),
('Hotel6'),
('Hotel7')

create table locations
(
    ID INT IDENTITY(1,1),
    Location geography
)

insert into locations (location) values
('Point(138.58 -34.92)'),
('POINT(138.59 -34.93)'),
('POINT(138.00 -34.00)'),
('POINT(138.57 -34.01)'),
('POINT(138.50 -34.03)'),
('POINT(138.49 -34.04)'),
('POINT(138.88 -34.04)')

select ln1.Name, ln2.Name, l1.location.STDistance(l2.Location)
FROM Locations l1
JOIN Locations l2 on l2.ID < l1.ID
JOIN LocationNames ln1 on ln1.ID = l1.ID
JOIN LocationNames ln2 on ln2.ID = l2.ID