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121 lines
4.1 KiB
Markdown
121 lines
4.1 KiB
Markdown
# ODBC {#table_engine-odbc}
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Allows ClickHouse to connect to external databases via [ODBC](https://en.wikipedia.org/wiki/Open_Database_Connectivity).
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To implement ODBC connection safely, ClickHouse uses the separate program `clickhouse-odbc-bridge`. If the ODBC driver is loaded directly from the `clickhouse-server` program, the problems in the driver can crash the ClickHouse server. ClickHouse starts the `clickhouse-odbc-bridge` program automatically when it is required. The ODBC bridge program is installed by the same package as the `clickhouse-server`.
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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 [ON CLUSTER cluster]
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(
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name1 [type1] [DEFAULT|MATERIALIZED|ALIAS expr1] [TTL expr1],
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name2 [type2] [DEFAULT|MATERIALIZED|ALIAS expr2] [TTL expr2],
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...
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)
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ENGINE = ODBC(connection_settings, external_database, external_table)
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```
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See the detailed description of the [CREATE TABLE](../../query_language/create.md#create-table-query) query.
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The table structure can be not the same as the source table structure:
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- Names of columns should be the same as in the source table, but you can use just some of these columns in any order.
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- Types of columns may differ from the types in the source table. ClickHouse tries to [cast](../../query_language/functions/type_conversion_functions.md#type_conversion_function-cast) values into the ClickHouse data types.
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**Engine Parameters**
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- `connection_settings` — Name of the section with connection settings in the `odbc.ini` file.
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- `external_database` — Name of a database in an external DBMS.
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- `external_table` — Name of a table in the `external_database`.
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## Usage Example
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**Getting data from the local MySQL installation via ODBC**
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This example is for linux Ubuntu 18.04 and MySQL server 5.7.
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Ensure that there are unixODBC and MySQL Connector are installed.
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By default (if installed from packages) ClickHouse starts on behalf of the user `clickhouse`. Thus, you need to create and configure this user at MySQL server.
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```
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sudo mysql
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mysql> CREATE USER 'clickhouse'@'localhost' IDENTIFIED BY 'clickhouse';
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mysql> GRANT ALL PRIVILEGES ON *.* TO 'clickhouse'@'clickhouse' WITH GRANT OPTION;
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```
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Then configure the connection in `/etc/odbc.ini`.
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```
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$ cat /etc/odbc.ini
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[mysqlconn]
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DRIVER = /usr/local/lib/libmyodbc5w.so
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SERVER = 127.0.0.1
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PORT = 3306
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DATABASE = test
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USERNAME = clickhouse
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PASSWORD = clickhouse
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```
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You can check the connection by the `isql` utility from the unixODBC installation.
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```
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isql -v mysqlconn
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+---------------------------------------+
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| Connected! |
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...
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```
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Table in MySQL:
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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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Table in ClickHouse, getting data from the MySQL table:
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```sql
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CREATE TABLE odbc_t
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(
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`int_id` Int32,
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`float_nullable` Nullable(Float32)
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)
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ENGINE = ODBC('DSN=mysqlconn', 'test', 'test')
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```
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```sql
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SELECT * FROM odbc_t
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```
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```text
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┌─int_id─┬─float_nullable─┐
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│ 1 │ ᴺᵁᴸᴸ │
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└────────┴────────────────┘
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```
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## See Also
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- [ODBC external dictionaries](../../query_language/dicts/external_dicts_dict_sources.md#dicts-external_dicts_dict_sources-odbc)
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- [ODBC table function](../../query_language/table_functions/odbc.md).
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[Original article](https://clickhouse.yandex/docs/en/operations/table_engines/jdbc/) <!--hide-->
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