mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-12 02:23:14 +00:00
132 lines
4.4 KiB
Markdown
132 lines
4.4 KiB
Markdown
---
|
|
toc_priority: 2
|
|
toc_title: ODBC
|
|
---
|
|
|
|
# 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](../../../sql-reference/data-types/nullable.md) data type.
|
|
|
|
## Creating a Table {#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](../../../sql-reference/statements/create/table.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](../../../sql-reference/functions/type-conversion-functions.md#type_conversion_function-cast) values to the ClickHouse data types.
|
|
- The [external_table_functions_use_nulls](../../../operations/settings/settings.md#external-table-functions-use-nulls) setting defines how to handle Nullable columns. Default value: 1. If 0, the table function does not make Nullable columns and inserts default values instead of nulls. This is also applicable for NULL values inside arrays.
|
|
|
|
**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 {#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 {#see-also}
|
|
|
|
- [ODBC external dictionaries](../../../sql-reference/dictionaries/external-dictionaries/external-dicts-dict-sources.md#dicts-external_dicts_dict_sources-odbc)
|
|
- [ODBC table function](../../../sql-reference/table-functions/odbc.md)
|
|
|
|
[Original article](https://clickhouse.tech/docs/en/engines/table-engines/integrations/odbc/) <!--hide-->
|