Fix ALIAS columns not applying timezone conversion for DateTime types in analyzer

[alexey-milovidov]

The analyzer used DataType::equals to check if a cast was needed for ALIAS columns, but DateTime and DateTime64 equals methods intentionally ignore timezone differences. This meant an alias like DateTime64(3, 'Europe/Berlin') ALIAS timestamp (where timestamp is DateTime64(3)) would skip the cast, returning the raw UTC value with just the timezone label changed — no actual timezone conversion.

Changed to getName() string comparison (matching the old interpreter behavior) so timezone differences are detected and a proper _CAST is applied.

Closes #76787

Changelog category (leave one):

• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes into CHANGELOG.md):

Fix ALIAS columns with DateTime/DateTime64 types not applying timezone conversion when the declared timezone differs from the expression timezone.

Documentation entry for user-facing changes

• Documentation is written (mandatory for new features)

[clickhouse-gh]

Workflow [PR], commit [a0b3a11]

Summary: ✅

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AI Review

Summary

This PR fixes a real analyzer correctness issue for ALIAS columns with DateTime/DateTime64 timezones by switching type-equality checks from equals (which intentionally ignores timezone) to getName-based comparison before applying _CAST. The change is small, targeted, and covered by a new stateless test that validates both DateTime64 and DateTime behavior. I did not find a high-confidence correctness, safety, or performance regression in the modified paths.

Missing context

• ⚠️ CI had not completed at review time (only pending workflow status was visible), so this review is code-and-tests based.

ClickHouse Rules

Item	Status	Notes
Deletion logging	➖
Serialization versioning	➖
Core-area scrutiny	✅
No test removal	✅
Experimental gate	➖
No magic constants	✅
Backward compatibility	✅
SettingsChangesHistory.cpp	➖
PR metadata quality	✅
Safe rollout	✅
Compilation time	✅

Final Verdict

• Status: ✅ Approve

[alexey-milovidov]

The fix LGTM

[clickhouse-gh]

LLVM Coverage Report

Metric	Baseline	Current	Δ
Lines	84.10%	84.20%	+0.10%
Functions	24.50%	24.50%	+0.00%
Branches	76.70%	76.80%	+0.10%

Changed lines: 92.86% (13/14) · Uncovered code

Full report · Diff report