問題描述

我的 SQLite 數據庫表中存儲了一些位置坐標.我想檢索距用戶當前位置 1 公里范圍內的位置.現在我正在從數據庫中獲取所有值，并編寫了一個方法來檢索我范圍內的值.這給我留下了很大的開銷，因為我的表可能包含 1000 多個坐標.

I have some location coordinates stored in my SQLite database table. I want to retrieve the locations within 1 km range from the use's current location. Right now I am fetching all values from database and have written a method to retrieve the values within my range. This leaves me great overhead as my table might contain more than 1000 coordinates.

所以我正在尋找一種更好的方法來做到這一點.是否可以直接使用 SELECT 查詢直接檢索我范圍內的位置?我發現 問題 1 和 問題 2 但不能找不到可能的解決方法.任何幫助將不勝感激.

So i am looking for a better way to do this. Is it possible to directly retrieve locations within my range directly using SELECT query? I found question 1 and question 2 but couldn't find a possible workaround.Any help will be greatly appreciated.

這是我現在的 SELECT 查詢:

This is my SELECT Query now :

String selectQuery = "SELECT  "+COLUMN_OBJECTID+","+COLUMN_OBJECTNAME_ENGLISH+"," 
                      +COLUMN_OBJECTNAME_ARABIC+","+COLUMN_OBJECTLATITUDE+","+COLUMN_OBJECTLONGITUDE+"," 
                              +COLUMN_OBJECTCATEGORYID+","+COLUMN_OBJECTADDRESS_ENGLISH+","+COLUMN_OBJECTADDRESS_ARABIC 
                              +" FROM " + TABLE_OBJECTLIST+" WHERE "+COLUMN_OBJECTCATEGORYID+"='"+categoryId+"' AND "+ 
                              ((userLat-Double.parseDouble(COLUMN_OBJECTLATITUDE))*(userLat-Double.parseDouble(COLUMN_OBJECTLATITUDE)) 
                                      +(userLong-Double.parseDouble(COLUMN_OBJECTLONGITUDE))*(userLong-Double.parseDouble(COLUMN_OBJECTLONGITUDE))<=range);

推薦答案

你可以寫一個帶有以下 where 條件的 SQL 查詢:

You can write a SQL query with following where condition :

where ( (my_lat - LAT)*(my_lat - LAT) + (my_lon - LON)*(my_lon - LON) ) <= 1KM

這個想法是使用畢達哥拉斯方法來計算近似位置并在此基礎上進行過濾.這里我沒有取平方根，因為我猜 SQLite 中的 SQL 函數沒有 sqrt.

The idea is that use Pythagoras method to calculate approx location and filter based on that. Here I have not taken the square root because I guess SQL functions in SQLite don't have sqrt.

這對近似計算很有用...

This is good for approximate calculations ...

我使用了以下 SQL 并且它工作正常......

I used following SQL and it worked ...

// Table with columns as String and Float
CREATE TABLE "locations" ("id" INTEGER PRIMARY KEY  AUTOINCREMENT  NOT NULL , "lat_string" VARCHAR, "long_string" VARCHAR, "lat_val" FLOAT, "long_val" FLOAT)

// Insert example data
INSERT INTO "locations" VALUES(1,'12.9587926','77.7477416',12.9587926,77.7477416);
INSERT INTO "locations" VALUES(2,'12.9973486','77.6967362',12.9973486,77.69673619999999);
INSERT INTO "locations" VALUES(3,'12.9715987','77.5945627',12.9715987,77.5945627);
INSERT INTO "locations" VALUES(4,'12.9629354','77.7122996',12.9629354,77.7122996);

// Select when column format is string. This works in SQLIte
SELECT id, ( (77.7580827 - long_string)*(77.7580827 - long_string) + (12.9905542 - lat_string)*(12.9905542 - lat_string) ) as dist FROM locations

// Select when column format is float. This works in SQLIte
SELECT id, ( (77.7580827 - long_val)*(77.7580827 - long_val) + (12.9905542 - lat_val)*(12.9905542 - lat_val) ) as dist FROM locations

這篇關于如何從 SQLite 數據庫中的用戶位置檢索特定范圍內的一組位置的文章就介紹到這了，希望我們推薦的答案對大家有所幫助，也希望大家多多支持html5模板網！