ClickHouse/docs/en/query_language/table_functions/mysql.md

# mysql

Allows `SELECT` queries to be performed on data that is stored on a remote MySQL server.

```sql
mysql('host:port', 'database', 'table', 'user', 'password'[, replace_query, 'on_duplicate_clause']);
```

**Parameters**

- `host:port` — MySQL server address.
- `database` — Remote database name.
- `table` — Remote table name.
- `user` — MySQL user.
- `password` — User password.
- `replace_query` — Flag that converts `INSERT INTO` queries to `REPLACE INTO`. If `replace_query=1`, the query is replaced.
- `on_duplicate_clause` — The `ON DUPLICATE KEY on_duplicate_clause` expression that is added to the `INSERT` query.

    Example: `INSERT INTO t (c1,c2) VALUES ('a', 2) ON DUPLICATE KEY UPDATE c2 = c2 + 1`, where `on_duplicate_clause` is `UPDATE c2 = c2 + 1`. See the MySQL documentation to find which `on_duplicate_clause` you can use with the `ON DUPLICATE KEY` clause.

    To specify `on_duplicate_clause` you need to pass `0` to the `replace_query` parameter. If you simultaneously pass `replace_query = 1` and `on_duplicate_clause`, ClickHouse generates an exception.

Simple `WHERE` clauses such as ` =, !=, >, >=, <, <=` are currently executed on the MySQL server.

The rest of the conditions and the `LIMIT` sampling constraint are executed in ClickHouse only after the query to MySQL finishes.

**Returned Value**

A table object with the same columns as the original MySQL table.

## Usage Example

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)
```

Selecting data from ClickHouse:

```sql
SELECT * FROM mysql('localhost:3306', 'test', 'test', 'bayonet', '123')
```
```text
┌─int_id─┬─int_nullable─┬─float─┬─float_nullable─┐
│      1 │         ᴺᵁᴸᴸ │     2 │           ᴺᵁᴸᴸ │
└────────┴──────────────┴───────┴────────────────┘
```

## See Also

- [The 'MySQL' table engine](../../operations/table_engines/mysql.md)
- [Using MySQL as a source of external dictionary](../dicts/external_dicts_dict_sources.md#dicts-external_dicts_dict_sources-mysql)

[Original article](https://clickhouse.yandex/docs/en/query_language/table_functions/mysql/) <!--hide-->