JDBC table engine

Allows ClickHouse to connect to external databases via JDBC.

clickhouse-jdbc-bridge contains experimental codes and is no longer supported. It may contain reliability issues and security vulnerabilities. Use it at your own risk. ClickHouse recommend using built-in table functions in ClickHouse which provide a better alternative for ad-hoc querying scenarios (Postgres, MySQL, MongoDB, etc).

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, external_database, external_table)

Engine Parameters

• datasource — 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 — Name of a database in an external DBMS, or, instead, an explicitly defined table schema (see examples).

• external_table — Name of the table in an external database or a select query like select * from table1 where column1=1.

• These parameters can also be passed using named collections.

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

┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
│      1 │         ᴺᵁᴸᴸ │     2 │           ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴────────────────┘

INSERT INTO jdbc_table(`int_id`, `float`)
SELECT toInt32(number), toFloat32(number * 1.0)
FROM system.numbers

See also

• JDBC table function.