fix(ibis): fix ClickHouse Decimal/Numeric and Nullable Type Mapping

[MarceloNunesAlves]

This PR addresses an issue in the ClickHouse data source connector where Decimal, Numeric, and Nullable data types were not being correctly mapped to Wren Engine's internal types.

Previously, the type mapping relied on exact string matches. When ClickHouse returned parameterized types like Decimal(15,2), the lookup in CLICKHOUSE_TYPE_MAPPING would fail, resulting in an UNKNOWN type and a warning log.

Changes

• Parameterized Type Handling: Updated the ClickHouse type adapter to strip precision and scale parameters (e.g., converting Decimal(18,4) to decimal) before performing the dictionary lookup.
• **Support for Numeric**: Added numeric as a valid alias for decimal in the ClickHouse type mapping.
• Nullable Support: Added logic to handle the Nullable(T) wrapper by extracting the inner type T before mapping.
• Updated Mapping Table: Expanded CLICKHOUSE_TYPE_MAPPING to ensure all variations of decimal and numeric types are captured.

Problem Flow (Example)

1. ClickHouse returns: Nullable(Decimal(15,2))
2. Normalization:

• Unwraps Nullable → Decimal(15,2)
• Removes parameters → decimal

3. Dictionary Lookup: Successfully finds decimal in CLICKHOUSE_TYPE_MAPPING.
4. Result: Correctly mapped to Wren DECIMAL type. ✅

Checklist

• I have confirmed that this change complies with the project's contribution guidelines.
• I have added tests to cover these type mapping scenarios.
• All existing tests passed.

Summary by CodeRabbit

Improvements

• Enhanced ClickHouse data source compatibility with improved type mapping for numeric and decimal data types
• Improved handling of nullable column types to ensure accurate data representation and compatibility
• Increased robustness when working with diverse ClickHouse database schemas

[coderabbitai]

📝 Walkthrough

Walkthrough

Added support for numeric column types in ClickHouse type mapping. Extended the type transformation logic to recognize decimal and numeric prefixes, handle Nullable type wrappers, and map them to corresponding RustWrenEngineColumnType values.

Changes

Cohort / File(s)	Summary
ClickHouse Type Mapping Enhancement ibis-server/app/model/metadata/clickhouse.py	Added "numeric" type to CLICKHOUSE_TYPE_MAPPING constant. Enhanced _transform_column_type function to detect and unwrap Nullable types recursively, and handle decimal/numeric type prefixes for direct column type mapping.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A numeric bloom in ClickHouse lands,
Where Nullable types fall into our hands,
Decimals unwrapped, mappings aligned,
New column types beautifully designed! ✨

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main
Title check	✅ Passed	The title 'fix(ClickHouse Decimal/Numeric and Nullable Type Mapping' accurately describes the main changes: it addresses type mapping issues for Decimal, Numeric, and Nullable types in ClickHouse.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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[goldmedal]

Thanks @MarceloNunesAlves. Makes sense to me 👍