v.22.4Improvement

Now Supports Metadata-Level ALTER MODIFY COLUMN for Arrays and Nullable Types

Official CH changelog text
Now some ALTER MODIFY COLUMN queries for Arrays and Nullable types can be done at metadata level without mutations. For example, alter from Array(Enum8('Option1'=1)) to Array(Enum8('Option1'=1, 'Option2'=2)). #35882 (alesapin).
Support for performing certain ALTER MODIFY COLUMN operations on Array and Nullable column types at the metadata level without requiring data mutations.

Why it matters

This feature addresses the need to efficiently modify complex column types such as arrays and nullable fields without triggering expensive data mutations, thus improving the speed and reducing the resource consumption of schema changes.

How to use it

Users can execute ALTER TABLE ... MODIFY COLUMN statements on supported Array and Nullable columns (e.g., adding new enum values inside an Array(Enum8(...))) directly, and the change will be applied at the metadata level without running mutations.

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