使用列值作为列名mysql [英] use column value as column name mysql

问题描述

我正在尝试使所有用户的半径都在5公里以内.这是我的表结构

I am trying to get all users in 5 KM radius. here is my table structure

id| location
-------------
1|  26.851791,75.781810
2|  26.860729,75.7633127
3|  34.057811,-84.239125

我写了一个查询以根据lat和long

I write a query to separate the location according to lat and long

SELECT SUBSTRING_INDEX( location, ',', 1 ) AS lat, SUBSTRING_INDEX( location, ',', -1 ) AS lng
FROM `users_test`
LIMIT 0 , 30

哪个工作正常，我得到的结果如下?

Which work fine and I got results as following

然后，根据以下博客，我编写一个查询以获取所有位于5KM Radius中的用户.

then I write a query to get all the users who are in 5KM Radius according to the following blog.

https://www.marketingtechblog.com/calculate-distance/

SELECT *,SUBSTRING_INDEX( location, ',', 1 ) AS lat, SUBSTRING_INDEX( location, ',', -1 ) AS lng,(((acos(sin(("26.851791"*pi()/180)) * sin((`lat`*pi()/180))+cos(("26.851791"*pi()/180)) * cos((`lat`*pi()/180)) * cos((("75.781810"- `lng`)*pi()/180))))*180/pi())*60*1.1515*1.609344) as distance
FROM `users_test`
WHERE distance >= "5"

但是我遇到以下错误.

#1054-字段列表"中的未知列"lat"

#1054 - Unknown column 'lat' in 'field list'

谁能告诉我我哪里错了.

can anyone tell me where I am wrong.

推荐答案

您不能在同一SELECT子句中引用列别名.您需要将其移动到子查询中.而且您不能在同一SELECT的WHERE子句中引用别名，您需要使用HAVING.

You can't refer to a column alias in the same SELECT clause. You need to move it into a subquery. And you can't refer to an alias in the WHERE clause of the same SELECT, you need to use HAVING.

SELECT *, (((acos(sin(("26.851791"*pi()/180)) * sin((`lat`*pi()/180))+cos(("26.851791"*pi()/180)) * cos((`lat`*pi()/180)) * cos((("75.781810"- `lng`)*pi()/180))))*180/pi())*60*1.1515*1.609344) as distance
FROM (SELECT *, 
        SUBSTRING_INDEX( location, ',', 1 ) AS lat, 
        SUBSTRING_INDEX( location, ',', -1 ) AS lng
      FROM users_test) x
HAVING distance > 5

我强烈建议您修正表格设计，将纬度和经度放在自己的列中，而不必每次都用逗号分开.

I strongly suggest you fix your table design to put the latitude and longitude in their own columns, instead of having to split on comma every time.

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