[C++] Multi argument operator kernel behavior for decimal columns

[asfimport]

This is a JIRA to discuss the behavior of operator kernels that require more than one decimal column input where the column types have a different scale parameter.

For example:

a: decimal(12, 2)
b: decimal(10, 3)

c = a + b

Arithmetic is the primary use case, but anything that needs to efficiently operate on decimal columns with different scales would require this functionality.

I imagine that @jacques-n and folks at Dremio have thought about and solved the problem in Java. If so, we should consider implementing this behavior in C++. Otherwise, I'll do a bit of reading and digging to see how existing systems efficiently handle this problem.

Reporter: Phillip Cloud / @cpcloud

Related issues:

• [C++][Compute] Add scalar arithmetic kernels for decimal inputs (is superceded by)

_{Note: This issue was originally created as ARROW-1761. Please see the migration documentation for further details.}

[asfimport]

Jacques Nadeau / @jacques-n:
Start by taking a look here.
https://github.com/dremio/dremio-oss/blob/master/sabot/kernel/src/main/java/com/dremio/exec/expr/fn/OutputDerivation.java

These are the notes that we have about our scale/precision behaviors (we're actually in the middle of reimplementing decimal using llvm). These are primarily modeled after MS SQL Server's behavior. We can share as we've reimplemented.

[asfimport]

Wes McKinney / @wesm:
This will need to be resolved once adding Decimal support to compute/kernels/scalar_arithmetic.cc

[asfimport]

Antoine Pitrou / @pitrou:
This was done as part of ARROW-12074 (for simple arithmetics).