Question about `day` transform result type

[lurnagao-dahua]

Apache Iceberg version

1.5.2 (latest release)

Query engine

None

Please describe the bug 🐞

Hi!
The transform name 'day' result type is 'int' in spec.md and partition-transforms
and the code in Days.java is:
@Override public Type getResultType(Type sourceType) { return Types.DateType.get(); }
So may I ask if the document was written incorrectly and the actual return type is date?

[ajantha-bhat]

Good catch. I think the spec is correct.
Now if we change it the schema will be different from old client and new client (compatibility issue).

I think it has to be handled as per 2.0 release.
Let us wait for others opinion.

[Fokko]

Hey @lurnagao-dahua Thanks for raising this, and @ajantha-bhat for jumping in here. This was discussed earlier in #10159 and points to a comment in #279 (comment).

Some historical context:

• int -> date in Update doc to state that day partition transform produces data type #447
• date -> int in Api: Fix transforms.day() returns a format document and javadoc #5980
• Discussed earlier this year in API: Fix day partition transform result type #9345

So the logical type is a date, but the physical type is still an int32, maybe we should make that more explicit? It seems to cause a lot of confusion. Looking forward to hearing what others think.

[ajantha-bhat]

@Fokko: Thanks for pointing out the previous discussions. I was certain that important topics like this had been covered before, but I couldn't find the relevant threads. I appreciate you sharing them. It's great to know that you bumped into this during the Python implementation 👍

[lurnagao-dahua]

Thank you everyone!