特定半徑內的郵編

Question

我正在查找SQL查詢以讓我檢索特定半徑內的ZipCodes。

我有一個名爲tblZip的表，其列爲：Zipcode,Lat（緯度），Long（經度）。

tblZip 

Zipcode | Lat | Long 
Short Text | Number | Number 

我已經檢查了一些其他的答案是建議使用Great-circle Distance但我似乎不明白它是如何工作的。我只是看到所有的轉換成弧度和度數而頭痛，我真的很想理解它，但是我對數學很不好。

我感謝您的幫助和指導。

PS：我正在使用Microsoft Access數據庫。

Answer 1

考慮在VBA函數中使用半正向公式（借用here）。然後讓它在你的SQL查詢中調用。甚至可以按照您的需求通​​過WHERE條款按距離過濾您的查詢。請注意：此解決方案僅適用於MSAccess.exe程序。您將無法通過ODBC/OLEDB從外部調用它。

而且由於您需要比較地理編碼，因此下面的SQL查詢使用交叉連接，其中每個記錄都與表中的每個其他記錄進行比較。另外，查詢避免了反向重複和相同匹配的配對，從而減小了大小。但是，如果表格很大，因爲交叉連接對自我返回N 記錄，即在重複過濾之前。

SQL

SELECT z1.Zipcode, z2.Zipcode, 
     GetDistance(z1.Lat, z1.Lon, z2.Lat, z2.Lon) As km_distance 
FROM tblZip z1, tblZip z2 
WHERE z1.Zipcode > z2.Zipcode 
AND GetDistance(s1.lat, s1.lon, s1.lat, s2.lon) <= 5; 

VBA（具有5 km或更小距離郵政編碼配對）（獨立模塊中保存）

Function GetDistance(lat1Degrees As Double, lon1Degrees As Double, lat2Degrees As Double, lon2Degrees As Double) As Double 

    Dim earthSphereRadiusKilometers As Double 
    Dim kilometerConversionToMilesFactor As Double 
    Dim lat1Radians As Double 
    Dim lon1Radians As Double 
    Dim lat2Radians As Double 
    Dim lon2Radians As Double 
    Dim AsinBase As Double 
    Dim DerivedAsin As Double 

    'Mean radius of the earth (replace with 3443.89849 to get nautical miles) 
    earthSphereRadiusKilometers = 6371 

    'Convert kilometers into miles (replace 0.621371 with 1 to keep in kilometers) 
    kilometerConversionToMilesFactor = 0.621371 

    'Convert each decimal degree to radians 
    lat1Radians = (lat1Degrees/180) * (4 * ATN(1)) 
    lon1Radians = (lon1Degrees/180) * (4 * ATN(1)) 
    lat2Radians = (lat2Degrees/180) * (4 * ATN(1)) 
    lon2Radians = (lon2Degrees/180) * (4 * ATN(1)) 

    AsinBase = Sin(Sqr(Sin((lat1Radians - lat2Radians)/2)^2 + Cos(lat1Radians) * Cos(lat2Radians) * Sin((lon1Radians - lon2Radians)/2)^2)) 
    DerivedAsin = (AsinBase/Sqr(-AsinBase * AsinBase + 1)) 

    'Get distance from [lat1,lon1] to [lat2,lon2] 
    GetMiles = Round(2 * DerivedAsin * (earthSphereRadiusKilometers * kilometerConversionToMilesFactor), 2) 

End Function