ODBC

Allows ClickHouse to connect to external databases via ODBC.

To implement ODBC connection safely, ClickHouse uses the separate program clickhouse-odbc-bridge. If the ODBC driver is loaded directly from the clickhouse-server program, the problems in the driver can crash the ClickHouse server. ClickHouse starts the clickhouse-odbc-bridge program automatically when it is required. The ODBC bridge program is installed by the same package as the clickhouse-server.

This engine supports the Nullable data type.

Creating a Table

CREATE TABLE [IF NOT EXISTS] [db.]table_name [ON CLUSTER cluster]
(
    name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [TTL expr1],
    name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2] [TTL expr2],
    ...
)
ENGINE = ODBC(connection_settings, external_database, external_table)

See the detailed description of the CREATE TABLE query.

The table structure can be not the same as the source table structure:

Names of columns should be the same as in the source table, but you can use just some of these columns in any order.
Types of columns may differ from the types in the source table. ClickHouse tries to cast values into the ClickHouse data types.

Engine 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.

Usage Example

Getting data from the local MySQL installation via ODBC

This example is for linux Ubuntu 18.04 and MySQL server 5.7.

Ensure that there are unixODBC and MySQL Connector are installed.

By default (if installed from packages) ClickHouse starts on behalf of the user clickhouse. Thus, you need to create and configure this user at 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 by 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)

Table in ClickHouse, getting data from the MySQL table:

CREATE TABLE odbc_t
(
    `int_id` Int32,
    `float_nullable` Nullable(Float32)
)
ENGINE = ODBC('DSN=mysqlconn', 'test', 'test')

SELECT * FROM odbc_t

┌─int_id─┬─float_nullable─┐
│      1 │           ᴺᵁᴸᴸ │
└────────┴────────────────┘

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ODBC

Creating a Table

Usage Example

See Also

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