[bjsneto]

Summary

• Normalize ClickHouseDecimal mantissa and scale before calculating the hash code.
• Add regression tests for numerically equal values with different scales.
• Add a changelog fragment for issue ClickHouseDecimal: GetHashCode depends on Scale, but Equals ignores Scale #639.

Problem

ClickHouseDecimal.Equals compares numeric values after aligning their scales, but
GetHashCode previously included the raw scale. As a result, values such as 1.5
and 1.5000 were equal but produced different hash codes.

This caused incorrect behavior in HashSet<ClickHouseDecimal>,
Dictionary<ClickHouseDecimal, TValue>, and LINQ operations such as Distinct
and GroupBy.

Fix

GetHashCode now hashes the canonical representation produced by removing trailing
fractional zeros while preserving the original Mantissa and Scale stored by the
instance.

Tests

• Added regression coverage for equal values with different scales.
• Verified HashSet<ClickHouseDecimal>.Contains.
• Verified that GetHashCode() does not change the stored representation.
• Ran the ClickHouse.Driver.Tests test suite.

Fixes #639

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Note

Low Risk
Localized change to hash computation with tests; behavior change only for previously inconsistent equal values in hash-based collections.

Overview
Fixes ClickHouseDecimal violating the Equals/GetHashCode contract when the same numeric value is stored with different mantissa/scale pairs (e.g. 1.5 vs 15000 at scale 4), which broke HashSet, Dictionary, and LINQ deduplication.

GetHashCode now hashes a normalized mantissa and scale (trailing fractional zeros stripped, same idea as equality), using local copies so the instance’s stored Mantissa and Scale are unchanged.

Adds regression tests for equal values across scales (matching hash codes and HashSet.Contains) and a changelog note for #639.

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