MySQL column not found despite being declared? - mysql

Question

This query works:
select d.*,
(6371 * 3.1415926 * SQRT((:lat - dl.lat) * (:lat - dl.lat) + COS(:lat / 57.2957795) * COS(dl.lat / 57.2957795) * (:long - dl.long) * (:long - dl.long)) / 180) as xdistance
from `dudes` as d
left join `dude_locations` as dl on (dl.id_dude = d.id)
where
(6371 * 3.1415926 * SQRT((:lat - dl.lat) * (:lat - dl.lat) + COS(:lat / 57.2957795) * COS(dl.lat / 57.2957795) * (:long - dl.long) * (:long - dl.long)) / 180) <= dl.distance
group by d.id
limit 20
However, this query throws a "column xdistance not found" error:
select d.*,
(6371 * 3.1415926 * SQRT((:lat - dl.lat) * (:lat - dl.lat) + COS(:lat / 57.2957795) * COS(dl.lat / 57.2957795) * (:long - dl.long) * (:long - dl.long)) / 180) as xdistance
from `dudes` as d
left join `dude_locations` as dl on (dl.id_dude = d.id)
where
xdistance <= dl.distance
group by d.id
limit 20
All I'm trying to do is make it so the same calculation isn't made twice. Is this possible?
Any help would be appreciated.

Answer 1

where
d.xdistance <= dl.distance

Answer 2

It is possible that the query you want is something like this:
select d.*,
MIN((6371 * 3.1415926 * SQRT((:lat - dl.lat) * (:lat - dl.lat) + COS(:lat / 57.2957795) * COS(dl.lat / 57.2957795) * (:long - dl.long) * (:long - dl.long)) / 180) ) as xdistance
from `dudes` as d left join
`dude_locations` as dl
on (dl.id_dude = d.id)
group by d.id
having xdistance <= min(dl.distance)
limit 20;