ClickHouse/docs/en/operations/table_engines/odbc.md
2020-01-30 13:34:55 +03:00

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