[Rust] Add integration tests for Decimal type

[asfimport]

We have basic decimal support, but we have not yet included decimals in the integration testing.

Reporter: Neville Dipale / @nevi-me
Assignee: Florian Müller / @sweb

PRs and other links:

• GitHub Pull Request #8784
• GitHub Pull Request #8880

_{Note: This issue was originally created as ARROW-10674. Please see the migration documentation for further details.}

[asfimport]

Florian Müller / @sweb:
Hey [~nevi_me],

 

I started to work on the IPC reader for decimal but I ran into an interesting issue, maybe you can help me with this:

As far as I can tell, the values used in arrow/testing/data/arrow-ipc-stream/integration/0.14.1/generated_decimal.arrow_file are encoded as little endian. I was under the impression that big endian is used. This is based on the documentation in the parquet crate. Does the encoding always differ for arrow serialization or am I missing something?

 

In addition, the type is Decimal(3,2), however the values are e.g. -11697. My understanding so far was (again this is probably just true for parquet) that this values does not fit in Decimal(3,2) but if it is actually -116.97 it should be Decimal(5, 2).

 

I am a bit out of my depth here, so if you have some documentation as to when I have to deal with which encoding, that would be very helpful.

[asfimport]

Jorge Leitão / @jorgecarleitao:
Issue resolved by pull request 8784
#8784