Added MySQL and ODBC Table Functions for Remote Database Access (Beta)

Why it matters

This feature provides native support for accessing remote databases directly from ClickHouse using MySQL and ODBC protocols. It solves the problem of needing to export or replicate data from external databases before querying it in ClickHouse, thus enabling seamless, on-demand querying of live remote data sources. This enhances interoperability, reduces ETL complexity, and allows more flexible data integration for users.

How to use it

To use the feature, you can query remote databases by using the mysql() and odbc() table functions or the corresponding MySQL and ODBC table engines in your SQL queries. For example, use

SELECT  FROM mysql('host:port', 'database', 'table', 'user', 'password')

to query a MySQL remote table. Similarly, use

SELECT  FROM odbc('DSN', 'table', 'user', 'password')

to query a remote database through ODBC. These functions can be used anywhere a table is expected, enabling integration of external data in ClickHouse queries.