How to effectively determine n places inside a circle?

Given this scenario:

• We have about 1,000,000 points worldwide, defined by longitude and latitude;
• We have a circle c based on the point pc (given by longitude and latitude) and radius rc
• We want to effectively determine which point is in the circle.

I am developing in C # and places stored on SQL Server 2008.

So, as I see it, I have these 3 options:

• Save locations as longitude floats and do calculations in C #.

• Store locations as geographic data types and perform calculations in SQL Server 2008 as follows:

  CREATE TABLE UserLocations
  [UserId] [bigint] NOT NULL,
  [CurrentLocation] [geography] NOT NULL
  
  ALTER PROCEDURE sp_GetCurrentUsersInRange
  @userPoint geography, 
  @RangeInMeters int
  AS
  BEGIN
  
  select  UserId from UserLocations
  where @userPoint.STDistance(CurrentLocation) <= @RangeInMeters
  and UserId <> @userId
  
  END
  

  Disadvantages: problems using geographic data with LinqToSQL and LinqToEntities.

  Advantages: using dbms processing power on big data and using SQL Server spatial index.

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