Nullable Columns Support for MySQL and ODBC Tables

Why it matters

This feature enables ClickHouse to correctly handle columns that can contain NULL values when working with external MySQL and ODBC tables. It solves the limitation where previously these columns could not be read or written accurately, improving interoperability and data consistency for users integrating ClickHouse with other database systems.

How to use it

Users can now define Nullable column types in their MySQL or ODBC table engines schema definitions as usual. ClickHouse will properly interpret and process NULL values from these tables without any additional configuration.