> ## Documentation Index
> Fetch the complete documentation index at: https://private-7c7dfe99-fix-nav-issues.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# MySQL dictionary source

> Configure MySQL as a dictionary source in ClickHouse.

Example of settings:

<Tabs>
  <Tab title="DDL">
    ```sql theme={null}
    SOURCE(MYSQL(
        port 3306
        user 'clickhouse'
        password 'qwerty'
        replica(host 'example01-1' priority 1)
        replica(host 'example01-2' priority 1)
        db 'db_name'
        table 'table_name'
        where 'id=10'
        invalidate_query 'SQL_QUERY'
        fail_on_connection_loss 'true'
        query 'SELECT id, value_1, value_2 FROM db_name.table_name'
        enable_compression 1
    ))
    ```
  </Tab>

  <Tab title="Configuration file">
    ```xml theme={null}
    <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>
          <fail_on_connection_loss>true</fail_on_connection_loss>
          <query>SELECT id, value_1, value_2 FROM db_name.table_name</query>
          <enable_compression>1</enable_compression>
      </mysql>
    </source>
    ```
  </Tab>
</Tabs>

<br />

Setting fields:

| Setting                   | Description                                                                                                                                                                                                                                                                                                                        |
| ------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `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. The syntax for conditions is the same as for `WHERE` clause in MySQL, for example, `id > 10 AND id < 20`. Optional.                                                                                                                                                                                        |
| `invalidate_query`        | Query for checking the dictionary status. Optional. Read more in the section [Refreshing dictionary data using LIFETIME](/reference/statements/create/dictionary/lifetime).                                                                                                                                                        |
| `fail_on_connection_loss` | Controls behavior of the server on connection loss. If `true`, an exception is thrown immediately if the connection between client and server was lost. If `false`, the server retries to fetch data at least three times before reporting an error. Note that retrying leads to increased response times. Default value: `false`. |
| `query`                   | The custom query. Optional.                                                                                                                                                                                                                                                                                                        |
| `enable_compression`      | Enables zlib compression for the MySQL protocol connection. When set to `1`, ClickHouse requests protocol-level compression from the MySQL server. Can also be set per-replica inside `<replica>`. Default value: `0`.                                                                                                             |

<Note>
  The `table` or `where` fields cannot be used together with the `query` field. And either one of the `table` or `query` fields must be declared.
</Note>

<Note>
  There is no explicit parameter `secure`. When establishing an SSL-connection security is mandatory.
</Note>

MySQL can be connected to on a local host via sockets. To do this, set `host` and `socket`.

Example of settings:

<Tabs>
  <Tab title="DDL">
    ```sql theme={null}
    SOURCE(MYSQL(
        host 'localhost'
        socket '/path/to/socket/file.sock'
        user 'clickhouse'
        password 'qwerty'
        db 'db_name'
        table 'table_name'
        where 'id=10'
        invalidate_query 'SQL_QUERY'
        fail_on_connection_loss 'true'
        query 'SELECT id, value_1, value_2 FROM db_name.table_name'
    ))
    ```
  </Tab>

  <Tab title="Configuration file">
    ```xml theme={null}
    <source>
      <mysql>
          <host>localhost</host>
          <socket>/path/to/socket/file.sock</socket>
          <user>clickhouse</user>
          <password>qwerty</password>
          <db>db_name</db>
          <table>table_name</table>
          <where>id=10</where>
          <invalidate_query>SQL_QUERY</invalidate_query>
          <fail_on_connection_loss>true</fail_on_connection_loss>
          <query>SELECT id, value_1, value_2 FROM db_name.table_name</query>
      </mysql>
    </source>
    ```
  </Tab>
</Tabs>