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99 lines
2.7 KiB
Markdown
99 lines
2.7 KiB
Markdown
---
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toc_priority: 34
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toc_title: JDBC表引擎
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---
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# JDBC {#table-engine-jdbc}
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允许CH通过 [JDBC](https://en.wikipedia.org/wiki/Java_Database_Connectivity) 连接到外部数据库。
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要实现JDBC连接，CH需要使用以后台进程运行的程序 [clickhouse-jdbc-bridge](https://github.com/ClickHouse/clickhouse-jdbc-bridge)。
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该引擎支持 [Nullable](../../../sql-reference/data-types/nullable.md) 数据类型。
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## 建表 {#creating-a-table}
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``` sql
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CREATE TABLE [IF NOT EXISTS] [db.]table_name
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(
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columns list...
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)
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ENGINE = JDBC(datasource_uri, external_database, external_table)
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```
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**引擎参数**
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- `datasource_uri` — 外部DBMS的URI或名字.
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URI格式: `jdbc:<driver_name>://<host_name>:<port>/?user=<username>&password=<password>`.
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MySQL示例: `jdbc:mysql://localhost:3306/?user=root&password=root`.
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- `external_database` — 外部DBMS的数据库名.
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- `external_table` — `external_database`中的外部表名或类似`select * from table1 where column1=1`的查询语句.
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## 用法示例 {#usage-example}
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通过mysql控制台客户端来创建表
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Creating a table in MySQL server by connecting directly with it’s console client:
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``` text
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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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在CH服务端创建表，并从中查询数据：
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``` sql
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CREATE TABLE jdbc_table
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(
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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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ENGINE JDBC('jdbc:mysql://localhost:3306/?user=root&password=root', 'test', 'test')
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```
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``` sql
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SELECT *
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FROM jdbc_table
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```
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``` text
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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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```
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``` sql
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INSERT INTO jdbc_table(`int_id`, `float`)
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SELECT toInt32(number), toFloat32(number * 1.0)
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FROM system.numbers
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```
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## 参见 {#see-also}
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- [JDBC表函数](../../../sql-reference/table-functions/jdbc.md).
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[原始文档](https://clickhouse.com/docs/en/operations/table_engines/jdbc/) <!--hide-->
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