查询来获取SQLite中基于RADIUS记录？ [英] Query to get records based on Radius in SQLite?

问题描述

我有这个疑问这确实做工精细MySQL中

I have this query which does work fine in MySQL

SELECT ((ACOS(SIN(12.345 * PI() / 180) * SIN(lat * PI() / 180) +
         COS(12.345 * PI() / 180) * COS(lat * PI() / 180) * COS((67.89 - lon) * 
         PI() / 180)) * 180 / PI()) * 60 * 1.1515 * 1.609344) AS distance, poi.* 
FROM poi
WHERE lang='eng' 
HAVING distance<='30'

距离在公里，输入经纬度= 12.345 和 LON = 67.89

在SQLite是3，我不能用它运行自定义的功能，因为它是在Android上。我也没有ACOS（）等等......因为这不是标准的SQLite的一部分。

The SQLite is 3, and I can't run custom functions with it as it's on Android. I also don't have acos() etc... as that is not part of the standard SQLite.

如何将上面的查询SQLite中？

How would be the above query in SQLite?

推荐答案

您可以创建4个新列，是罪和 COS纬度和 LON 。由于 COS（A + B）= COS一个COS b - 罪过罪过b ，以及正弦和余弦的其他出现如 SIN（12.345 * PI （）/ 180）运行查询之前，可以计算出程序，大大的距离EX pression减少了一些形式 P * SIN_LAT + Q * COS_LAT + ... 可通过sqlite3的处理。

You can create 4 new columns, being sin and cos of lat and lon. Since cos(a+b) = cos a cos b - sin a sin b, and other appearances of sin and cos like SIN(12.345 * PI() / 180) can be calculated in the program before running the query, the big "distance" expression reduces to something of the form P * SIN_LAT + Q * COS_LAT + ... that can be handled by SQLite3.

顺便说一下，也见<一href="http://stackoverflow.com/questions/2352320/sqlite-on-android-how-to-create-a-sqlite-dist-db-function-to-be-used-in-the-ap">http://stackoverflow.com/questions/2352320/sqlite-on-android-how-to-create-a-sqlite-dist-db-function-to-be-used-in-the-ap.

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