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Posted to github@arrow.apache.org by "stuartcarnie (via GitHub)" <gi...@apache.org> on 2023/02/06 23:47:03 UTC
[GitHub] [arrow-datafusion] stuartcarnie opened a new issue, #5206: Add SQL function overload log(b,x) for logarithm of x to base b
stuartcarnie opened a new issue, #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206
**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, $x$ to base $b$.
**Describe the solution you'd like**
Add an overload to the `log` function, which takes two arguments. Using PostgreSQL for inspiration per [the documentation](https://www.postgresql.org/docs/current/functions-math.html):
> `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**
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[GitHub] [arrow-datafusion] stuartcarnie commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "stuartcarnie (via GitHub)" <gi...@apache.org>.
stuartcarnie commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425012018
In the case of the `LOG` function, if there is a single argument, it is assumed to be LOG $x$ base 10:
> ```
> log ( numeric ) → numeric
> log ( double precision ) → double precision
> Base 10 logarithm
> log(100) → 2
```
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[GitHub] [arrow-datafusion] comphead commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "comphead (via GitHub)" <gi...@apache.org>.
comphead commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425007441
@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
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[GitHub] [arrow-datafusion] alamb closed issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
URL: https://github.com/apache/arrow-datafusion/issues/5206
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[GitHub] [arrow-datafusion] stuartcarnie commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "stuartcarnie (via GitHub)" <gi...@apache.org>.
stuartcarnie commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425022133
@comphead awesome, thanks for doing that!
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[GitHub] [arrow-datafusion] comphead commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "comphead (via GitHub)" <gi...@apache.org>.
comphead commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425011893
Thanks @stuartcarnie with `log` I came out to the similar solution, inspecting `len()` :) but was wondering if we already have something more elegant to provide default values, seems we dont have it yet
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[GitHub] [arrow-datafusion] stuartcarnie commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "stuartcarnie (via GitHub)" <gi...@apache.org>.
stuartcarnie commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425012606
@comphead no worries – I looked for other solutions too, but that is all I could find for now.
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[GitHub] [arrow-datafusion] stuartcarnie commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "stuartcarnie (via GitHub)" <gi...@apache.org>.
stuartcarnie commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425009998
@comphead there are already examples in DF of this, for example the `ltrim` function takes 1 or 2 arguments:
https://github.com/apache/arrow-datafusion/blob/ac876dbc9729b16e272e00496c51e53d9f649173/datafusion/physical-expr/src/string_expressions.rs#L355-L369
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[GitHub] [arrow-datafusion] comphead commented on issue #5206: Add SQL function overload `LOG(base, x)` for logarithm of x to base
Posted by "comphead (via GitHub)" <gi...@apache.org>.
comphead commented on issue #5206:
URL: https://github.com/apache/arrow-datafusion/issues/5206#issuecomment-1425015548
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 function
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