Same query but different result when ran in different database servers - sql

Question

I have a local environment running MariaDB server version 10.2.14 and a production environment running MariaDB server version 10.1.40.
When running a calculation based on the haversine formula to calculate distance between 2 geolocations, my local environment returns 0 as the result, but the prod environment returns null.
A sample query is below:
select (acos(cos(radians((41.480473))) * cos(radians(41.480473)) *
cos(radians((-81.630990)) - radians(-81.630990)) +
sin(radians((41.480473))) * sin(radians(41.480473))) * 3958.755
) as distance
The result should be zero because it is essentially trying to get the distance between 2 locations with the same geolocation info.
Can anyone shed some light why my prod environment is giving me a null value when running the above sample instead of zero?

Answer 1

The difference comes from rounding errors for the outmost acos-function. The other system may give you exactly 1 while the other system may give you bit over 1 due to rounding errors. Valid parameters for acos are from 1 is 0 and acos value > 1 is NULL.
You can use ROUND before the outmost acos and make the calculation a function for easier use:
create function f_distance_in_miles(
in_lat1 decimal(9,7),
in_long1 decimal(9,7),
in_lat2 decimal(9,7),
in_long2 decimal(9,7)
)
returns float
deterministic
begin
declare v_i real;
set v_i = cos(radians(in_lat1)) * cos(radians(in_lat2)) * cos(radians(in_long1)
- radians(in_long2))
+ sin(radians(in_lat1)) * sin(radians(in_lat2));
if (v_i<-1) then
set v_i = -1;
elseif (v_i>1) then
set v_i = 1;
end if;
return acos(v_i)*3958.755;
end
And then use it like:
select f_distance_in_miles(41.480473, -81.630990, 41.480473, -81.630990)