v.21.10Improvements

ALTER MODIFY COLUMN to Nullable(T) No Longer Requires Mutation

Official CH changelog text
Now ALTER MODIFY COLUM T to Nullable(T) doesn't require mutation. #27787 (victorgao).
Now ALTER MODIFY COLUMN allows changing a column's type to Nullable(T) without requiring a mutation.

Why it matters

This feature improves schema modification efficiency by enabling users to make columns nullable directly through ALTER MODIFY COLUMN without triggering costly mutations, thus reducing downtime and resource usage during schema changes.

How to use it

To make a column nullable, use the ALTER TABLE <table> MODIFY COLUMN <column> Nullable(<Type>) statement. The change will be applied instantly without initiating a mutation process.

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