Skip to main content

JDBC

Allows ClickHouse to connect to external databases via JDBC.

To implement the JDBC connection, ClickHouse uses the separate program clickhouse-jdbc-bridge that should run as a daemon.

This engine supports the Nullable data type.

Creating a Table​

CREATE TABLE [IF NOT EXISTS] [db.]table_name
(
columns list...
)
ENGINE = JDBC(datasource_uri, external_database, external_table)

Engine Parameters

  • datasource_uri β€” URI or name of an external DBMS.

    URI Format: jdbc:<driver_name>://<host_name>:<port>/?user=<username>&password=<password>. Example for MySQL: jdbc:mysql://localhost:3306/?user=root&password=root.

  • external_database β€” Database in an external DBMS.

  • external_table β€” Name of the table in external_database or a select query like select * from table1 where column1=1.

Usage Example​

Creating a table in MySQL server by connecting directly with it’s console client:

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)

Creating a table in ClickHouse server and selecting data from it:

CREATE TABLE jdbc_table
(
`int_id` Int32,
`int_nullable` Nullable(Int32),
`float` Float32,
`float_nullable` Nullable(Float32)
)
ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
SELECT *
FROM jdbc_table
β”Œβ”€int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
β”‚ 1 β”‚ ᴺᡁᴸᴸ β”‚ 2 β”‚ ᴺᡁᴸᴸ β”‚
β””β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”΄β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”€β”˜
INSERT INTO jdbc_table(`int_id`, `float`)
SELECT toInt32(number), toFloat32(number * 1.0)
FROM system.numbers

See Also​

Original article