Optimize calculations in this query? - mysql

Question

What's the best way to optimize this query?
$tripsNearLocation = mysqli_query($con,
"SELECT * FROM (
SELECT *
, ( 3959 * acos( cos(" . $latRad . ")
* cos( radians( startingLatitude ) )
* cos( radians( startingLongitude )
- (" . $longRad . ") )
+ sin(" . $latRad . ")
* sin( radians( startingLatitude ) ) ) )
AS distance FROM trips
) as query
WHERE distance < 10
ORDER BY distance LIMIT 0 , 10;");
With 50,000 rows it takes it a second or two to finish. Should I add a different query that eliminates all rows that aren't even in the "close range" of the coordinates inputted then calculate the remaining rows? Say if the latitude coordinate inputted is 67, eliminate all rows with latitude coordinate that isn't from 65-69.
Or add a "state column" where it removes all rows from calculations if they aren't in the same state?
Or just deal with the 2 seconds of calculations? I'm worried the database may contain more that 100,000 rows and it will take to long to excute.

Answer 1

Plan A: For 100K rows, you might get away with just narrowing down by latitude. That is,
calculate the degrees latitude that corresponds to "10" units of distance
Have INDEX(startingLatitude)
Add to the WHERE clause to limit it to startingLatitude plus/minus "10". Perhaps your example is AND startingLatitude BETWEEN 65 AND 69.
If you are thinking about using INDEX(lat, lng), it is not as simple. See if Lat is good enough.
Plan B: Next choice will involve lat and lng, plus a subquery. And version 5.6 would be beneficial. It's something like this (after including INDEX(lat, lng, id)):
SELECT ... FROM (
SELECT id FROM tbl
WHERE lat BETWEEN...
AND lng BETWEEN... ) x
JOIN tbl USING (id)
WHERE ...;
For various reasons, Plan B is only slightly better than Plan A.
Plan C: If you are going to need millions of rows, you will need my pizza parlor algorithm. This involves a Stored Procedure to repeatedly probe, looking for enough rows. It also involves PARTITIONing to get a crude 2D index.
Plans A and B are O(sqrt(N)); Plan C is O(1). That is, for Plans A and B, if you quadruple the number of rows, you double the time taken. Plan C does not get slower. (It sounded like your code is O(N) -- double the rows = double the time.)

Answer 2

This is how I ended up solving it incase people need to reference this in the future.
$tripsNearLocation = mysqli_query($con, "SELECT * FROM (
SELECT *, (3959 * acos(cos(" . $latRad . ") * cos(radians(startingLatitude))
* cos(radians(startingLongitude) - (" . $longRad . ")) + sin(" . $latRad . ")
* sin(radians(startingLatitude)))) AS distance FROM (
SELECT * FROM trips_test WHERE startingLatitude BETWEEN " .
($locationLatitude - 1) . " AND " . ($locationLatitude + 1) . ") as query1)
as query2 WHERE distance < 10 ORDER BY distance LIMIT 0 , 10;");
Although I will accept Rick James' answer as he helped me get to this solution.