SQL：无法将nvarchar转换为复杂查询中的数字

Question

I need to get the nearest airport in my database table from the current users position. I found this formula: https://de.scribd.com/presentation/2569355/Geo-Distance-Search-with-MySQL#page=7

So there are a few differences between the formula described in the link above and my current situation: The example was in MySQL, I'm using MS SQL (not a problem, I guess). lat and lon are considered to be database columns with numeric data type, but for some reason the database table was created with two corresponding columns of type varchar .

My problem is: When I want to use an ORDER BY clause, it throws Error converting data type nvarchar to numeric , without it, it works. I did some research on what rubbish was inserted as string and migrated it so that I just have some empty values.

I can't take all because I only need one. But if I do TOP 1 without ORDER BY I don't get any airport rather than the nearest airport. Does anyone know how to fix the query?

Thanks in advance!

SELECT TOP 1
  temp.Distance
FROM (
  SELECT
    (
      3956 * 2 * ASIN(
          SQRT(
              POWER(
                  SIN((53.6349994 - abs(CAST(latitude_deg AS numeric))) * pi() / 180 / 2), 2) + COS(53.6349994 * pi()/180) * COS(abs(CAST(latitude_deg AS numeric)) * pi()/180) * POWER(SIN((10.0117336 - CAST(longitude_deg AS numeric)) * pi()/180 / 2), 2) ))) AS Distance
  FROM Airport_Airports
  WHERE
    isnumeric(longitude_deg) = 1 AND isnumeric(latitude_deg) = 1 AND
    longitude_deg LIKE '%[^0-9.]%' AND latitude_deg LIKE '%[^0-9.]%'
) AS temp
WHERE
  temp.Distance < 50000
Order BY
  temp.Distance

Answer 1

First, this logic doesn't make sense:

WHERE isnumeric(longitude_deg) = 1 AND
      isnumeric(latitude_deg) = 1 AND
      longitude_deg LIKE '%[^0-9.]%' AND
      latitude_deg LIKE '%[^0-9.]%'

The like is looking for non-numeric characters. I think you intend:

WHERE isnumeric(longitude_deg) = 1 AND
      isnumeric(latitude_deg) = 1 AND
      longitude_deg NOT LIKE '%[^0-9.]%' AND
      latitude_deg NOT LIKE '%[^0-9.]%'

This ensures that the values are numeric.

The solution to your problem -- at least in SQL Server 2012+ -- is to use try_convert() or try_cast() :

  (3956 * 2 * ASIN(
      SQRT(
          POWER(
              SIN((53.6349994 - abs(try_convert(numeric, latitude_deg))) * pi() / 180 / 2), 2) + COS(53.6349994 * pi()/180) * COS(abs(try_convert(numeric, latitude_deg)) * pi()/180) * POWER(SIN((10.0117336 - try_convert(numeric, longitude_deg)) * pi()/180 / 2), 2) ))) AS Distance

This will prevent any conversion errors.

You shouldn't use just numeric . Use either a floating point representation or something with decimal places, say numeric(20, 10) .

The reason this occurs with the order by is because of the SQL optimizer. You clearly have some lat/long values that do not convert correctly to a numeric . SQL Server allows itself to re-arrange operations, so the conversion might take place before the filtering by the where clause. This is part of the overall query optimization.