使用WHERE子句在距离经度和纬度的距​​离范围内查找POI [英] Using WHERE clause to find POI within a range of distance from Longitude and Latitude

问题描述

我使用下面的sql代码来找出离设置坐标最近的'ALL'poi，但是我想找出具体的poi而不是所有的poi。当我尝试使用where子句时，我得到一个错误，它不起作用，这是我目前卡住的地方，因为我只使用一个表来处理所有poi的所有坐标。

I'm using following sql code to find out 'ALL' poi closest to the set coordinates, but I would want to find out specific poi instead of all of them. When I try to use the where clause I get an error and it doesn't work and this is where I'm currently stuck, since I only use one table for all the coordinates off all poi's.

SET @orig_lat=55.4058;  
SET @orig_lon=13.7907; 
SET @dist=10;
SELECT 
    *, 
    3956 * 2 * ASIN(SQRT(POWER(SIN((@orig_lat -abs(latitude)) * pi()/180 / 2), 2) 
    + COS(@orig_lat * pi()/180 ) * COS(abs(latitude) * pi()/180) 
    * POWER(SIN((@orig_lon - longitude) * pi()/180 / 2), 2) )) as distance 
FROM geo_kulplex.sweden_bobo
HAVING distance < @dist 
ORDER BY distance limit 10;

推荐答案

问题是您无法引用别名列（距离在这种情况下）在中选择或其中条款。例如，你不能这样做：

The problem is that you can not reference an aliased column (distancein this case) in a select or where clause. For example, you can't do this:

select a, b, a + b as NewCol, NewCol + 1 as AnotherCol from table
where NewCol = 2

这两个操作都会失败：在试图处理 NewCol + 1 时选择语句，并且在其中语句中选择当试图处理 NewCol = 2 。

This will fail in both: the select statement when trying to process NewCol + 1 and also in the where statement when trying to process NewCol = 2.

有两种方法可以解决这个问题：

There are two ways to solve this:

1）将参考值替换为计算值本身。示例：

1) Replace the reference by the calculated value itself. Example:

select a, b, a + b as NewCol, a + b + 1 as AnotherCol from table
where  a + b = 2

2）使用外部选择语句：

2) Use an outer select statement:

select a, b, NewCol, NewCol + 1 as AnotherCol from (
    select a, b, a + b as NewCol from table
) as S
where NewCol = 2

现在，考虑到你的巨大而不是非常人性化的计算栏:)我认为你应该选择最后一个选项来提高可读性：

Now, given your HUGE and not very human-friendly calculated column :) I think you should go for the last option to improve readibility:

SET @orig_lat=55.4058;  
SET @orig_lon=13.7907; 
SET @dist=10;

SELECT * FROM (
  SELECT 
    *, 
    3956 * 2 * ASIN(SQRT(POWER(SIN((@orig_lat -abs(latitude)) * pi()/180 / 2), 2) 
    + COS(@orig_lat * pi()/180 ) * COS(abs(latitude) * pi()/180) 
    * POWER(SIN((@orig_lon - longitude) * pi()/180 / 2), 2) )) as distance 
  FROM geo_kulplex.sweden_bobo
) AS S
WHERE distance < @dist
ORDER BY distance limit 10;

编辑：正如@Kaii在下面提到的那样，扫描。根据您要处理的数据量，您可能想避免这种情况，并选择第一个选项，该选项的执行速度会更快。

As @Kaii mentioned below this will result in a full table scan. Depending on the amount of data you will be processing you might want to avoid that and go for the first option, which should perform faster.

这篇关于使用WHERE子句在距离经度和纬度的距​​离范围内查找POI的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！