Calculating distance between two points (Latitude, Longitude)

Since you're using SQL Server 2008, you have the geography data type available, which is designed for exactly this kind of data:

DECLARE @source geography = 'POINT(0 51.5)'
DECLARE @target geography = 'POINT(-3 56)'

SELECT @source.STDistance(@target)

Gives

----------------------
538404.100197555

(1 row(s) affected)

Telling us it is about 538 km from (near) London to (near) Edinburgh.

Naturally there will be an amount of learning to do first, but once you know it it's far far easier than implementing your own Haversine calculation; plus you get a LOT of functionality.

If you want to retain your existing data structure, you can still use STDistance, by constructing suitable geography instances using the Point method:

DECLARE @orig_lat DECIMAL(12, 9)
DECLARE @orig_lng DECIMAL(12, 9)
SET @orig_lat=53.381538 set @orig_lng=-1.463526

DECLARE @orig geography = geography::Point(@orig_lat, @orig_lng, 4326);

SELECT *,
    @orig.STDistance(geography::Point(dest.Latitude, dest.Longitude, 4326)) 
       AS distance
--INTO #includeDistances
FROM #orig dest

The below function gives distance between two geocoordinates in miles

create function [dbo].[fnCalcDistanceMiles] (@Lat1 decimal(8,4), @Long1 decimal(8,4), @Lat2 decimal(8,4), @Long2 decimal(8,4))
returns decimal (8,4) as
begin
declare @d decimal(28,10)
-- Convert to radians
set @Lat1 = @Lat1 / 57.2958
set @Long1 = @Long1 / 57.2958
set @Lat2 = @Lat2 / 57.2958
set @Long2 = @Long2 / 57.2958
-- Calc distance
set @d = (Sin(@Lat1) * Sin(@Lat2)) + (Cos(@Lat1) * Cos(@Lat2) * Cos(@Long2 - @Long1))
-- Convert to miles
if @d <> 0
begin
set @d = 3958.75 * Atan(Sqrt(1 - power(@d, 2)) / @d);
end
return @d
end 

The below function gives distance between two geocoordinates in kilometres

CREATE FUNCTION dbo.fnCalcDistanceKM(@lat1 FLOAT, @lat2 FLOAT, @lon1 FLOAT, @lon2 FLOAT)
RETURNS FLOAT 
AS
BEGIN

    RETURN ACOS(SIN(PI()*@lat1/180.0)*SIN(PI()*@lat2/180.0)+COS(PI()*@lat1/180.0)*COS(PI()*@lat2/180.0)*COS(PI()*@lon2/180.0-PI()*@lon1/180.0))*6371
END

The below function gives distance between two geocoordinates in kilometres using Geography data type which was introduced in sql server 2008

DECLARE @g geography;
DECLARE @h geography;
SET @g = geography::STGeomFromText('LINESTRING(-122.360 47.656, -122.343 47.656)', 4326);
SET @h = geography::STGeomFromText('POINT(-122.34900 47.65100)', 4326);
SELECT @g.STDistance(@h);

Usage:

select [dbo].[fnCalcDistanceKM](13.077085,80.262675,13.065701,80.258916)

Reference: Ref1,Ref2

It looks like Microsoft invaded brains of all other respondents and made them write as complicated solutions as possible. Here is the simplest way without any additional functions/declare statements:

SELECT geography::Point(LATITUDE_1, LONGITUDE_1, 4326).STDistance(geography::Point(LATITUDE_2, LONGITUDE_2, 4326))

Simply substitute your data instead of LATITUDE_1, LONGITUDE_1, LATITUDE_2, LONGITUDE_2 e.g.:

SELECT geography::Point(53.429108, -2.500953, 4326).STDistance(geography::Point(c.Latitude, c.Longitude, 4326))
from coordinates c

Create Function [dbo].[DistanceKM] 
( 
      @Lat1 Float(18),  
      @Lat2 Float(18), 
      @Long1 Float(18), 
      @Long2 Float(18)
)
Returns Float(18)
AS
Begin
      Declare @R Float(8); 
      Declare @dLat Float(18); 
      Declare @dLon Float(18); 
      Declare @a Float(18); 
      Declare @c Float(18); 
      Declare @d Float(18);
      Set @R =  6367.45
            --Miles 3956.55  
            --Kilometers 6367.45 
            --Feet 20890584 
            --Meters 6367450 


      Set @dLat = Radians(@lat2 - @lat1);
      Set @dLon = Radians(@long2 - @long1);
      Set @a = Sin(@dLat / 2)  
                 * Sin(@dLat / 2)  
                 + Cos(Radians(@lat1)) 
                 * Cos(Radians(@lat2))  
                 * Sin(@dLon / 2)  
                 * Sin(@dLon / 2); 
      Set @c = 2 * Asin(Min(Sqrt(@a))); 

      Set @d = @R * @c; 
      Return @d; 

End
GO

Usage:

select dbo.DistanceKM(37.848832506474, 37.848732506474, 27.83935546875, 27.83905546875)

Outputs:

0,02849639

You can change @R parameter with commented floats.

As you're using SQL 2008 or later, I'd recommend checking out the GEOGRAPHY data type. SQL has built in support for geospatial queries.

e.g. you'd have a column in your table of type GEOGRAPHY which would be populated with a geospatial representation of the coordinates (check out the MSDN reference linked above for examples). This datatype then exposes methods allowing you to perform a whole host of geospatial queries (e.g. finding the distance between 2 points)

In addition to the previous answers, here is a way to calculate the distance inside a SELECT:

CREATE FUNCTION Get_Distance
(   
    @La1 float , @Lo1 float , @La2 float, @Lo2 float
)
RETURNS TABLE 
AS
RETURN 
    -- Distance in Meters
    SELECT GEOGRAPHY::Point(@La1, @Lo1, 4326).STDistance(GEOGRAPHY::Point(@La2, @Lo2, 4326))
    AS Distance
GO

Usage:

select Distance
from Place P1,
     Place P2,
outer apply dbo.Get_Distance(P1.latitude, P1.longitude, P2.latitude, P2.longitude)

Scalar functions also work but they are very inefficient when computing large amount of data.

I hope this might help someone.