Question

I have the next query for getting addresses within a given distance and given postal code. Distance is calculated, based upon longitude and latitude data.

In this example i have replaced the user-input for just values (lat=52.64, long=6.88 en desired distance=10km)

the query:

SELECT *,
ROUND( SQRT( POW( ( (69.1/1.61) * ('52.64' - latitude)), 2) + POW(( (53/1.61) * ('6.88' - longitude)), 2)), 1) AS distance
FROM lp_relations_addresses distance
WHERE distance < 10
 ORDER BY `distance`  DESC

gives unknown column distance as error message.
when leaving out the where clausule i get every record of the table including their calculated distance. In this case i have to fetch the whole table.

How do i get only the desired records to fetch??

Thanks in advance for any comment!

Answer 1

You can’t reference an alias in the select clause from another part of the sql statement. You need to put the whole expression in your where clause:

WHERE
    ROUND( SQRT( POW( ( (69.1/1.61) * ('52.64' - latitude)), 2)
        + POW(( (53/1.61) * ('6.88' - longitude)), 2)), 1) < 10

A cleaner solution would be to use a sub-query to generate the calculated data:

  SELECT *, distance
    FROM (
       SELECT *,
           ROUND( SQRT( POW( ( (69.1/1.61) * ('52.64' - latitude)), 2)
               + POW(( (53/1.61) * ('6.88' - longitude)), 2)), 1) AS distance
           FROM lp_relations_addresses
       ) d
   WHERE d.distance < 10
ORDER BY d.distance DESC

Demo: http://www.sqlize.com/q96p2mCwnJ