How to calculate square root in sqlite

Question

I need to calculate an euclidean distance in a sqlite database.

Does anyone know how to calculate square roots in sqlite beside writing and loading a dynamic library for

Answer 1

This is an approximation of sqrt for numbers under 10000. It can be extended for arbitrary numbers, and can be extended to arbitrary precision as needed. This kind of tabular interpolation is what happens in most fast implementations anyway:

case when weight >= 1 and weight<=10 then 1+0.240253073*(weight-1) 
     when weight>=10 and weight<=100 then 3.16227766+0.075974693*(weight-10) 
     when weight>=100 and weight<=1000 then 10+0.024025307*(weight-100)      
     else 31.6227766+0.007597469 *(weight-1000) end

And there's the curious fact that each factor you use in such a power-of-10 square root interpolation table is 0.316227766 times the previous one - so you can make this work for an arbitrarily large number, or even stuff a table full of these values to make it work for any number. (Could that lead to some compression here?)

Or this cute one for log10 of integers, using the length function (an interpolation table might work better here, but I like that log10 and length() are similar, and that this works for any integer - no interpolation needed.

 ((length(x)+length(x*2)+length(x*3)
  +length(x*4)+length(x*5))/5.0)-1.0

A better math head than I can probably come up with better and denser approximations. Considering that most sqrt functions in c use approximations anyway - this is a pretty good solution.

This is the only native way of doing it.