Question

I have a list of stores with their post codes. What I need to do is when a user types in a postcode on the webpage it search the db and then finds the closest 10 to that postcode.

example of data i have:

ID  = 1
Store =Halfords 
Address 1 =Unit 6b
Address 2 = Braidfute Retail Park   
Address 3   = Lanark    
Address 4 =South Lanarkshire
Postal Code = ML11 9AE
Lat = 55.6711692810059
Long = -3.77314400672913

I am able to convert the postcode into longitude and latitude, what query do i need to run to find stores within 10miles in ym table of this cord

Answer 1

Firstly, you’ll need the lat/lon of each postcode and store those in a table along with a geospatial representation (GEOGRAPHY, or GEOMETRY datatype). When a post code is entered by the user, you can the look up that post code in your db to find it’s location.

You’ll also need to store a GEOGRAPHY/GEOMETRY representation of each of the stores lat/lons you currently have.

Based on that, you can use all of SQL Server’s geospatial functionality to perform geospatial searches.

I’ve made available on GitHub a .NET app that will import the free Ordnance Survey postcode dataset (all post codes in GB) into SQL Server, converting all the Eastings/Northings provided by it, into lat/lon and then creating a geography column. I have a full blog post on that here. The end result would be used like this:

DECLARE @home GEOGRAPHY
SELECT @home = GeoLocation 
FROM dbo.PostCodeData 
WHERE OutwardCode = 'AB12' AND InwardCode = '3CD' -- Postcode entered by user

-- find all stores within 10 miles of the entered postcode
SELECT *
FROM dbo.Stores
WHERE GeoLocation.STDistance(@home) <= (10 * 1609) -- 1609 = approx metres in 1 mile

Hopefully, this will be a good starting point.