ClickHouse/docs/en/operations/table_engines/jdbc.md
BayoNet 3ff89198b7 DOCAPI-6207: JDBC engine EN description (#5112)
* DOCAPI-6207: JDBC engine EN description.

* DOCAPI-6207: Edits after review.
2019-05-08 01:50:37 +03:00

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# JDBC
Allows ClickHouse to connect to external databases via [JDBC](https://en.wikipedia.org/wiki/Java_Database_Connectivity).
To implement JDBC connection, ClickHouse uses the separate program [clickhouse-jdbc-bridge](https://github.com/alex-krash/clickhouse-jdbc-bridge). You should run it as a daemon.
This engine supports the [Nullable](../../data_types/nullable.md) 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` — A name of the table in `external_database`.
## Usage Example
Creating a table in MySQL (using native MySQL engine):
```
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)
```
Selecting data from the table in ClickHouse:
```
CREATE TABLE jdbc_table ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
Ok.
DESCRIBE TABLE jdbc_table
┌─name───────────────┬─type───────────────┬─default_type─┬─default_expression─┐
│ int_id │ Int32 │ │ │
│ int_nullable │ Nullable(Int32) │ │ │
│ float │ Float32 │ │ │
│ float_nullable │ Nullable(Float32) │ │ │
└────────────────────┴────────────────────┴──────────────┴────────────────────┘
10 rows in set. Elapsed: 0.031 sec.
SELECT *
FROM jdbc_table
┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
│ 1 │ ᴺᵁᴸᴸ │ 2 │ ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴────────────────┘
1 rows in set. Elapsed: 0.055 sec.
```
## See Also
- [JDBC table function](../../query_language/table_functions/jdbc.md).