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81 lines
3.0 KiB
Markdown
81 lines
3.0 KiB
Markdown
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# JDBC
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Allows ClickHouse to connect to external databases via [JDBC](https://en.wikipedia.org/wiki/Java_Database_Connectivity).
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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.
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This engine supports the [Nullable](../../data_types/nullable.md) data type.
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## Creating a Table
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```
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CREATE TABLE [IF NOT EXISTS] [db.]table_name ENGINE = JDBC(dbms_uri, external_database, external_table)
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```
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**Engine Parameters**
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- `dbms_uri` — URI of an external DBMS.
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Format: `jdbc:<driver_name>://<host_name>:<port>/?user=<username>&password=<password>`.
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Example for MySQL: `jdbc:mysql://localhost:3306/?user=root&password=root`.
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- `external_database` — Database in an external DBMS.
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- `external_table` — A name of the table in `external_database`.
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## Usage Example
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Creating a table in MySQL (using native MySQL engine):
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```
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mysql> CREATE TABLE `test`.`test` (
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-> `int_id` INT NOT NULL AUTO_INCREMENT,
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-> `int_nullable` INT NULL DEFAULT NULL,
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-> `float` FLOAT NOT NULL,
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-> `float_nullable` FLOAT NULL DEFAULT NULL,
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-> PRIMARY KEY (`int_id`));
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Query OK, 0 rows affected (0,09 sec)
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mysql> insert into test (`int_id`, `float`) VALUES (1,2);
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Query OK, 1 row affected (0,00 sec)
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mysql> select * from test;
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+--------+--------------+-------+----------------+
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| int_id | int_nullable | float | float_nullable |
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+--------+--------------+-------+----------------+
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| 1 | NULL | 2 | NULL |
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+--------+--------------+-------+----------------+
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1 row in set (0,00 sec)
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```
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Selecting data from the table in ClickHouse:
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```
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CREATE TABLE jdbc_table ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
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Ok.
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DESCRIBE TABLE jdbc_table
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┌─name───────────────┬─type───────────────┬─default_type─┬─default_expression─┐
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│ int_id │ Int32 │ │ │
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│ int_nullable │ Nullable(Int32) │ │ │
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│ float │ Float32 │ │ │
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│ float_nullable │ Nullable(Float32) │ │ │
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└────────────────────┴────────────────────┴──────────────┴────────────────────┘
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10 rows in set. Elapsed: 0.031 sec.
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SELECT *
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FROM jdbc_table
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┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
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│ 1 │ ᴺᵁᴸᴸ │ 2 │ ᴺᵁᴸᴸ │
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└────────┴──────────────┴───────┴────────────────┘
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1 rows in set. Elapsed: 0.055 sec.
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```
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## See Also
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- [JDBC table function](../../query_language/table_functions/jdbc.md).
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