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
#include "StorageMySQL.h"
#if USE_MYSQL
#include <Storages/StorageFactory.h>
#include <Storages/transformQueryForExternalDatabase.h>
#include <Formats/MySQLBlockInputStream.h>
#include <Interpreters/evaluateConstantExpression.h>
#include <Core/Settings.h>
#include <Interpreters/Context.h>
#include <DataTypes/DataTypeString.h>
#include <DataStreams/IBlockOutputStream.h>
#include <Formats/FormatFactory.h>
#include <Common/parseAddress.h>
#include <IO/Operators.h>
#include <IO/WriteHelpers.h>
#include <Parsers/ASTLiteral.h>
#include <mysqlxx/Transaction.h>
#include <Processors/Sources/SourceFromInputStream.h>
#include <Processors/Pipe.h>
#include <Common/parseRemoteDescription.h>
namespace DB
{
namespace ErrorCodes
{
    extern const int NUMBER_OF_ARGUMENTS_DOESNT_MATCH;
    extern const int BAD_ARGUMENTS;
}
static String backQuoteMySQL(const String & x)