> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-fix-nav-issues.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.
> Allows ClickHouse to connect to external databases via JDBC.
# JDBC table engine
export const CloudNotSupportedBadge = () => {
return
Not supported in ClickHouse Cloud
;
};
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](https://en.wikipedia.org/wiki/Java_Database_Connectivity).
To implement the JDBC connection, ClickHouse uses the separate program [clickhouse-jdbc-bridge](https://github.com/ClickHouse/clickhouse-jdbc-bridge) that should run as a daemon.
This engine supports the [Nullable](/reference/data-types/nullable) data type.
Creating a table
```sql theme={null}
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:://:/?user=&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](/concepts/features/configuration/server-config/named-collections).
Usage example
Creating a table in MySQL server by connecting directly with it's console client:
```text theme={null}
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:
```sql theme={null}
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')
```
```sql theme={null}
SELECT *
FROM jdbc_table
```
```text theme={null}
┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
│ 1 │ ᴺᵁᴸᴸ │ 2 │ ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴────────────────┘
```
```sql theme={null}
INSERT INTO jdbc_table(`int_id`, `float`)
SELECT toInt32(number), toFloat32(number * 1.0)
FROM system.numbers
```