Repository navigation
Add SQL function overload LOG(base, x) for logarithm of x to base #5206
Description
Is your feature request related to a problem or challenge? Please describe what you are trying to do.
As a user, I would like to determine the logarithm of a value,
Describe the solution you'd like
Add an overload to the log function, which takes two arguments. Using PostgreSQL for inspiration per the documentation:
log ( b numeric, x numeric ) → numeric
Logarithm of$x$ to base$b$
log(2.0, 64.0) → 6.0000000000000000
Describe alternatives you've considered
DataFusion strives for PostgreSQL compatibility, so it makes sense to use the PostgreSQL solution.
Additional context
Reacted by Andrew Lamb
Activity
[-]Add SQL function overload log(b,x) for logarithm of x to base b[/-][+]Add SQL function overload `LOG(x, base)` for logarithm of $x$ to base $b$[/+][-]Add SQL function overload `LOG(x, base)` for logarithm of $x$ to base $b$[/-][+]Add SQL function overload `LOG(x, base)` for logarithm of x to base[/+][-]Add SQL function overload `LOG(x, base)` for logarithm of x to base[/-][+]Add SQL function overload `LOG(base, x)` for logarithm of x to base[/+]comphead commentedon Feb 10, 2023
@alamb on top of my head we dont have overloaded scalar functions yet?
We know how to to create different aliases for the same function, but not overloading
stuartcarnie commentedon Feb 10, 2023
@comphead there are already examples in DF of this, for example the
ltrimfunction takes 1 or 2 arguments:https://github.com/apache/arrow-datafusion/blob/ac876dbc9729b16e272e00496c51e53d9f649173/datafusion/physical-expr/src/string_expressions.rs#L355-L369
comphead commentedon Feb 10, 2023
Thanks @stuartcarnie with
logI came out to the similar solution, inspectinglen():) but was wondering if we already have something more elegant to provide default values, seems we dont have it yetstuartcarnie commentedon Feb 10, 2023
In the case of the$x$ base 10:
LOGfunction, if there is a single argument, it is assumed to be LOGstuartcarnie commentedon Feb 10, 2023
@comphead no worries – I looked for other solutions too, but that is all I could find for now.
comphead commentedon Feb 10, 2023
Thats okay, I'll implement it using
len()but going forward probably we may want to think how we can substitute default values, in case of different signatures for the same scalar functionstuartcarnie commentedon Feb 10, 2023
@comphead awesome, thanks for doing that!