apache / apache/datafusion

Nested types and extension types are not supported in `Statistics` / `ColumnStatistics`

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#20,707 0 comments 1 reaction 0 assignees View on GitHub
enhancement
Dominant language
Rust
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Avg merge
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Merged PRs (30d)
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Description

### Is your feature request related to a problem or challenge?

The current `ColumnStatistics` structure is not able to represent nested types (e.g., list, map, or struct) for which statistics are present in Parquet data sources and perhaps others as well.

https://github.com/apache/datafusion/blob/d025869526e5c7c2c32d5f6318a634522d44a538/datafusion/common/src/stats.rs#L724-L752

In addition to list/struct/map statistics, the `Statistics` struct can't represent statistics for extension types. Three extension types for which we can get statistics from Parquet files are geometry, geography, and variant; however, there is no place to put them in the Statistics so they are dropped.

One approach for doing this is in https://github.com/apache/datafusion/pull/20589 , although I wonder if something dynamic could work as well (e.g., a trait with methods for the transformations that are currently hard coded for a fixed set of types).

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Contributor guide

Open the contributing guide

Research direction

Start with datafusion/common/src/stats.rs, especially the ColumnStatistics and Statistics definitions referenced in the issue, then review the approach in pull request 20589 and how Parquet statistics are handled. Done means nested list, map, and struct statistics plus geometry, geography, and variant extension-type statistics can be represented without being dropped.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
data
Issue type
Feature
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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