Create test table:
`CREATE TABLE test (`id` Int32) ENGINE = MySQL('localhost:3306', '', 'test', 'user', 'pass')`

Attempt insert:
`INSERT INTO test VALUES(1)`

CH sending SQL:
`INSERT INTO ``.`test` (`id`) VALUES (1)`

"``." - sending empty database name in generated SQL

However SELECT statement working with empty database name correctrly

P.S.
This can be useful when working with databases such as sphinx
{
    auto columns = getActualTableStructure(context);
    auto res = StorageMySQL::create(
        StorageID(getDatabaseName(), table_name),
        std::move(*pool),
        remote_database_name,
        remote_table_name,
        replace_query,
        on_duplicate_clause,
        columns,
        ConstraintsDescription{},
        context);
    pool.reset();
    res->startup();
    return res;
}
void registerTableFunctionMySQL(TableFunctionFactory & factory)
{
    factory.registerFunction<TableFunctionMySQL>();
}
}
#endif