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25.8.15 Stable backport of #84770: Handle NULLs in ALTER MODIFY COLUMN#1344

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zvonand merged 4 commits intoreleases/25.8.15from
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Jan 30, 2026
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25.8.15 Stable backport of #84770: Handle NULLs in ALTER MODIFY COLUMN#1344
zvonand merged 4 commits intoreleases/25.8.15from
backports/25.8.15/84770

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@zvonand zvonand commented Jan 27, 2026 •
edited by CarlosFelipeOR
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Changelog category (leave one):

  • Backward Incompatible Change

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

ALTER MODIFY COLUMN now requires explicit DEFAULT when converting nullable columns to non-nullable types. Previously such ALTERs could get stuck with cannot convert null to not null errors, now NULLs are replaced with column's default expression (ClickHouse#84770 by @vdimir)

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Exclude tests:

  • Fast test
  • Integration Tests
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  • Stateful tests
  • Performance tests
  • All with ASAN
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  • All Regression
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Regression jobs to run:

  • Fast suites (mostly <1h)
  • Aggregate Functions (2h)
  • Alter (1.5h)
  • Benchmark (30m)
  • ClickHouse Keeper (1h)
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@vdimir @zvonand
Merge pull request ClickHouse#84770 from ClickHouse/vdimir/modify_col…
08f97b7 
…umn_null_to_default

Handle NULLs in ALTER MODIFY COLUMN
@zvonand zvonand mentioned this pull request Jan 27, 2026
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github-actions bot commented Jan 27, 2026 •
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Workflow [PR], commit [e8ea542]

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zvonand commented Jan 30, 2026

S3 fails: Altinity/clickhouse-regression#93

Aggregate fails: uniqTheta was updated in upstream, not related, test will be updated separately by QA team

@zvonand zvonand merged commit 89bfe4f into releases/25.8.15 Jan 30, 2026
378 of 394 checks passed
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CarlosFelipeOR commented Feb 2, 2026

QA Verification

Changes Reviewed:

  • Core logic (inplaceBlockConversions.cpp): Adds handling for nullable → non-nullable column conversions by requiring explicit DEFAULT and using ifNull() to replace NULLs
  • New test added: 03575_modify_column_null_to_default.sql - covers main scenarios including error cases
  • Existing test fixed: 02662_sparse_columns_mutations_1.sql - updated to comply with new behavior

Verification Criteria:

Criteria Status
Upstream PR approved and merged ✅
Backport applies cleanly ✅
CI passing* (including the new 03575_modify_column_null_to_default.sql) ✅
New test covers the change ✅
No unintended modifications ✅

* Remaining Failures

Notes:

  • Additional test flakiness fix for test_async_load_databases included via merge
    No manual testing required - upstream validation and CI coverage are sufficient for this backport.

Adding verified label.

@CarlosFelipeOR CarlosFelipeOR added the verified Verified by QA label Feb 2, 2026
@DimensionWieldr DimensionWieldr mentioned this pull request Feb 3, 2026
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@svb-alt svb-alt added 25.8.16 25.8.16 Stable 25.8.16.10001 25.8.16.10001 Stable and removed 25.8.15 25.8.15.10001 labels Feb 5, 2026
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@zvonand @CarlosFelipeOR @svb-alt @vdimir @azat