How to limit a MySQL Distance Query - sql

Question

I'm trying to preform a distance calculation to return a listing of places within a certain distance. This is based on using a zip code database and determining the distance from the origin to each location. What I want to do is limit the results to be within a certain distance from the origin, but I'm having trouble with my MySQL query. Here's the basic query:
SELECT *,
ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude)) + COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude)) * COS(RADIANS(-88.462832 - zip_longitude))))) * 69.09 AS distance
FROM locations
LEFT JOIN zip_codes USING (zip_code)
ORDER BY distance ASC
This works great and gives me all the info for each location including the distance from the origin zip code...exactly what I want. However, I want to limit the results to fall within a certain distance (i.e., WHERE distance<=50).
My question and problem is I can't figure out where to include (WHERE distance<=50) into the query above to make it all work. Everything I've tried gives me an error message. Any help would be great.

Answer 1

You have two options:
Restate the logic in the WHERE clause so you can filter by it:
SELECT *,
ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude)) + COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude)) * COS(RADIANS(-88.462832 - zip_longitude))))) * 69.09 AS distance
FROM locations
LEFT JOIN zip_codes USING (zip_code)
WHERE (ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude)) + COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude)) * COS(RADIANS(-88.462832 - zip_longitude))))) * 69.09) <= 50
ORDER BY distance
This is the better choice, because it requires only one pass over the data. Sadly, it requires you to duplicate the logic -- if you were using the information in the GROUP BY or HAVING clause, MySQL supports referencing a column alias in those.
Use a subquery:
SELECT x.*
FROM (SELECT *,
ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude)) + COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude)) * COS(RADIANS(-88.462832 - zip_longitude))))) * 69.09 AS distance
FROM locations
LEFT JOIN zip_codes USING (zip_code)) x
WHERE x.distance <= 50
ORDER BY x.distance

Answer 2

A simple solution is to wrap your query in another query and put the condition and order there. This should work:
SELECT * FROM (
SELECT *, ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude)) + COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude)) * COS(RADIANS(-88.462832 - zip_longitude))))) * 69.09 AS distance FROM locations LEFT JOIN zip_codes USING (zip_code)
) WHERE distance <= 50 ORDER BY distance ASC
The middle line is your query without the ORDER BY

Answer 3

The simplest solution is actually using HAVING instead of WHERE, also i moved the last bracket of your ROUND function behind the 69.09, which gives you a higher precision in calculation but still returns a rounded number:
SELECT *,
ROUND(DEGREES(ACOS(SIN(RADIANS(42.320271)) * SIN(RADIANS(zip_latitude))
+ COS(RADIANS(42.320271)) * COS(RADIANS(zip_latitude))
* COS(RADIANS(-88.462832 - zip_longitude)))) * 69.09,2) AS distance
FROM locations
LEFT JOIN zip_codes USING (zip_code)
HAVING distance <= 50
ORDER BY distance ASC
So basically your query was fine, you just need to add the HAVING clause and you may want to fix that rounding to get better results. In my project i used following very similar formula discarding the outer DEGREES function and multiplying by earths circumference:
ROUND(ACOS(SIN(RADIANS('42.320271')) * SIN(RADIANS(zip_latitude))
+ COS(RADIANS('42.320271')) * COS(RADIANS(zip_latitude))
* COS(RADIANS(zip_longitude - '-88.462832'))) * 3963.190592,3) AS distance
and by changing the multiplier at the end, you have kilometers instead of miles:
ROUND(ACOS(SIN(RADIANS('42.320271')) * SIN(RADIANS(zip_latitude))
+ COS(RADIANS('42.320271')) * COS(RADIANS(zip_latitude))
* COS(RADIANS(zip_longitude - '-88.462832'))) * 6378.137,3) AS distance