使用sql查詢經緯度的半徑搜索

Question

在下面的查詢中，什麼是「cos（弧度（lat）」或「cos（弧度（lng）或」弧度（lat）「）？弧度（）功能嗎？

SELECT id, (3959 * acos(cos(radians(37)) 
       * cos(radians(lat)) 
       * cos(radians(lng) 
       - radians(-122)) + sin(radians(37)) 
       * sin(radians(lat)))) AS distance 
FROM markers 
HAVING distance < 25 
ORDER BY distance LIMIT 20 OFFSET 0; 

Answer 1

圓形功能這裏（cos()，sin()）取角度以弧度（2 *在一個圓圈裨弧度），但該角度以度表示（360度的圓），所以Radians()函數將Degrees轉換爲Radians，以便循環函數將給出正確結果。

Answer 2

DECLARE @CurrentLocation geography; 
SET @CurrentLocation = geography::Point(12.822222, 80.222222, 4326) 

SELECT * , Round (GeoLocation.STDistance(@CurrentLocation),0) AS Distance FROM [Landmark] 
WHERE GeoLocation.STDistance(@CurrentLocation)<= 2000 -- 2 Km 

精彩教程：

http://www.sql-server-helper.com/sql-server-2008/convert-latitude-longitude-to-geography-point.aspx