[Feature] Chained tables should allow set fallback rules for non-existent partitions.

[blackflash997997]

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• I searched in the issues and found nothing similar.

Motivation

when using chain tables:
my partitions :
branch_snapshot: 20260101
branch_delta: 20260102、20260104

so i using: select count(1) from table where dt=20260103 is 0
but in a scenario, It should return the most recent partition from the beginning of the timeline,
like above, should return data in 20260102
not 0.

Solution

add a configuration, allow user to decide whether to fallback to the most recent partition from the beginning of the timeline

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!

[Aitozi]

For this case, I think we should support to mark the partition 20260103 is exist, In this way, we could express the 20260103 is equal to the 20260102 full data