Question

I have table places

place_id | city | country_code | zipcode | lat | lon

Now I want to show places that are within 25 miles of place A. Place A has place_id 1.

SELECT * 
FROM `places` 
WHERE ( 3959 * acos( cos( radians((SELECT lat FROM places WHERE place_id=1)) ) * cos( radians( lat ) ) * cos( radians( lon ) - radians((SELECT lon FROM places WHERE place_id=1)) ) + sin( radians((SELECT lat FROM places WHERE place_id=1)) ) * sin( radians( lat ) ) ) ) < 25;

This works ok, but there are two the same subqueries

SELECT lat FROM places WHERE place_id=1

Is it possible to optimize this query to not have two the same subqueries but make them into 1?

Answer 1

Your three subqueries will execute for every row in the outer table.

What you can do is convert those subqueries to a single JOIN which will only execute once for the entire query in order to find the latitude and longitude of place_id 1:

SELECT a.* 
FROM   places a
JOIN   (SELECT lat, lon FROM places WHERE place_id = 1) b ON
       (3959 * acos( cos( radians(b.lat) ) * cos( radians( a.lat ) ) * cos( radians( a.lon ) - radians(b.lon) ) + sin( radians(b.lat) ) * sin( radians( a.lat ) ) ) ) < 25;