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 ENGINE = JDBC(dbms_uri, external_database, external_table)
Engine Parameters
-
dbms_uri
— URI of an external DBMS.Format:
jdbc:<driver_name>://<host_name>:<port>/?user=<username>&password=<password>
. Example for MySQL:jdbc:mysql://localhost:3306/?user=root&password=root
. -
external_database
— Database in an external DBMS. external_table
— Name of the table inexternal_database
.
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 ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
DESCRIBE TABLE jdbc_table
┌─name───────────────┬─type───────────────┬─default_type─┬─default_expression─┐ │ int_id │ Int32 │ │ │ │ int_nullable │ Nullable(Int32) │ │ │ │ float │ Float32 │ │ │ │ float_nullable │ Nullable(Float32) │ │ │ └────────────────────┴────────────────────┴──────────────┴────────────────────┘
SELECT * FROM jdbc_table
┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐ │ 1 │ ᴺᵁᴸᴸ │ 2 │ ᴺᵁᴸᴸ │ └────────┴──────────────┴───────┴────────────────┘