# odbc {#table_functions-odbc} Returns table that is connected via [ODBC](https://en.wikipedia.org/wiki/Open_Database_Connectivity). ``` odbc(connection_settings, external_database, external_table) ``` Parameters: - `connection_settings` — Name of the section with connection settings in the `odbc.ini` file. - `external_database` — Name of a database in an external DBMS. - `external_table` — Name of a table in the `external_database`. To safely implement ODBC connections, ClickHouse uses a separate program `clickhouse-odbc-bridge`. If the ODBC driver is loaded directly from `clickhouse-server`, driver problems can crash the ClickHouse server. ClickHouse automatically starts `clickhouse-odbc-bridge` when it is required. The ODBC bridge program is installed from the same package as the `clickhouse-server`. The fields with the `NULL` values from the external table are converted into the default values for the base data type. For example, if a remote MySQL table field has the `INT NULL` type it is converted to 0 (the default value for ClickHouse `Int32` data type). ## Usage example **Getting data from the local MySQL installation via ODBC** This example is checked for Ubuntu Linux 18.04 and MySQL server 5.7. Ensure that unixODBC and MySQL Connector are installed. By default (if installed from packages), ClickHouse starts as user `clickhouse`. Thus you need to create and configure this user in the MySQL server. ``` sudo mysql mysql> CREATE USER 'clickhouse'@'localhost' IDENTIFIED BY 'clickhouse'; mysql> GRANT ALL PRIVILEGES ON *.* TO 'clickhouse'@'clickhouse' WITH GRANT OPTION; ``` Then configure the connection in `/etc/odbc.ini`. ``` $ cat /etc/odbc.ini [mysqlconn] DRIVER = /usr/local/lib/libmyodbc5w.so SERVER = 127.0.0.1 PORT = 3306 DATABASE = test USERNAME = clickhouse PASSWORD = clickhouse ``` You can check the connection using the `isql` utility from the unixODBC installation. ``` isql -v mysqlconn +---------------------------------------+ | Connected! | | | ... ``` Table in MySQL: ``` mysql> CREATE TABLE `test`.`test` ( -> `int_id` INT NOT NULL AUTO_INCREMENT, -> `int_nullable` INT NULL DEFAULT NULL, -> `float` FLOAT NOT NULL, -> `float_nullable` FLOAT NULL DEFAULT NULL, -> PRIMARY KEY (`int_id`)); Query OK, 0 rows affected (0,09 sec) mysql> insert into test (`int_id`, `float`) VALUES (1,2); Query OK, 1 row affected (0,00 sec) mysql> select * from test; +--------+--------------+-------+----------------+ | int_id | int_nullable | float | float_nullable | +--------+--------------+-------+----------------+ | 1 | NULL | 2 | NULL | +--------+--------------+-------+----------------+ 1 row in set (0,00 sec) ``` Retrieving data from the MySQL table in ClickHouse: ```sql SELECT * FROM odbc('DSN=mysqlconn', 'test', 'test') ``` ```text ┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐ │ 1 │ 0 │ 2 │ 0 │ └────────┴──────────────┴───────┴────────────────┘ ``` ## See Also - [ODBC external dictionaries](../../query_language/dicts/external_dicts_dict_sources.md#dicts-external_dicts_dict_sources-odbc) - [ODBC table engine](../../operations/table_engines/odbc.md). [Original article](https://clickhouse.yandex/docs/en/query_language/table_functions/jdbc/)