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2.6 KiB
2.6 KiB
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(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
(
`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 │
└────────┴──────────────┴───────┴────────────────┘