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

  1. CREATE TABLE [IF NOT EXISTS] [db.]table_name
  2. 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 in external_database.

Usage Example

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

  1. mysql> CREATE TABLE `test`.`test` (
  2.     ->   `int_id` INT NOT NULL AUTO_INCREMENT,
  3.     ->   `int_nullable` INT NULL DEFAULT NULL,
  4.     ->   `float` FLOAT NOT NULL,
  5.     ->   `float_nullable` FLOAT NULL DEFAULT NULL,
  6.     ->   PRIMARY KEY (`int_id`));
  7. Query OK, 0 rows affected (0,09 sec)
  9. mysql> insert into test (`int_id`, `float`) VALUES (1,2);
  10. Query OK, 1 row affected (0,00 sec)
  12. mysql> select * from test;
  13. +--------+--------------+-------+----------------+
  14. | int_id | int_nullable | float | float_nullable |
  15. +--------+--------------+-------+----------------+
  16. |      1 |         NULL |     2 |           NULL |
  17. +--------+--------------+-------+----------------+
  18. 1 row in set (0,00 sec)

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

  1. CREATE TABLE jdbc_table ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
  3. Ok.
  5. DESCRIBE TABLE jdbc_table
  7. ┌─name───────────────┬─type───────────────┬─default_type─┬─default_expression─┐
  8. │ int_id             │ Int32              │              │                    │
  9. │ int_nullable       │ Nullable(Int32)    │              │                    │
  10. │ float              │ Float32            │              │                    │
  11. │ float_nullable     │ Nullable(Float32)  │              │                    │
  12. └────────────────────┴────────────────────┴──────────────┴────────────────────┘
  14. 10 rows in set. Elapsed: 0.031 sec.
  16. SELECT *
  17. FROM jdbc_table
  19. ┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
  20. │      1 │         ᴺᵁᴸᴸ │     2 │           ᴺᵁᴸᴸ │
  21. └────────┴──────────────┴───────┴────────────────┘
  23. 1 rows in set. Elapsed: 0.055 sec.

See Also

Original article