mysql - ClickHouse Documentation

Allows SELECT and INSERT queries to be performed on data that are stored on a remote MySQL server.

Syntax

mysql({host:port, database, table, user, password[, replace_query, on_duplicate_clause] | named_collection[, option=value [,..]]})

Arguments

Argument	Description
`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`. Possible values: - `0` - The query is executed as `INSERT INTO`. - `1` - The query is executed as `REPLACE INTO`.
`on_duplicate_clause`	The `ON DUPLICATE KEY on_duplicate_clause` expression that is added to the `INSERT` query. Can be specified only with `replace_query = 0` (if you simultaneously pass `replace_query = 1` and `on_duplicate_clause`, ClickHouse generates an exception). Example: `INSERT INTO t (c1,c2) VALUES ('a', 2) ON DUPLICATE KEY UPDATE c2 = c2 + 1;` `on_duplicate_clause` here is `UPDATE c2 = c2 + 1`. See the MySQL documentation to find which `on_duplicate_clause` you can use with the `ON DUPLICATE KEY` clause.

Arguments also can be passed using named collections. In this case host and port should be specified separately. This approach is recommended for production environment. 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. Supports multiple replicas that must be listed by |. For example:

SELECT name FROM mysql(`mysql{1|2|3}:3306`, 'mysql_database', 'mysql_table', 'user', 'password');

SELECT name FROM mysql(`mysql1:3306|mysql2:3306|mysql3:3306`, 'mysql_database', 'mysql_table', 'user', 'password');

Returned value

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

Some data types of MySQL can be mapped to different ClickHouse types - this is addressed by query-level setting mysql_datatypes_support_level

In the INSERT query to distinguish table function mysql(...) from table name with column names list, you must use keywords FUNCTION or TABLE FUNCTION. See examples below.

Examples

Table in MySQL:

mysql> CREATE TABLE `test`.`test` (
    ->   `int_id` INT NOT NULL AUTO_INCREMENT,
    ->   `float` FLOAT NOT NULL,
    ->   PRIMARY KEY (`int_id`));

mysql> INSERT INTO test (`int_id`, `float`) VALUES (1,2);

mysql> SELECT * FROM test;
+--------+-------+
| int_id | float |
+--------+-------+
|      1 |     2 |
+--------+-------+

Selecting data from ClickHouse:

SELECT * FROM mysql('localhost:3306', 'test', 'test', 'bayonet', '123');

Or using named collections:

CREATE NAMED COLLECTION creds AS
        host = 'localhost',
        port = 3306,
        database = 'test',
        user = 'bayonet',
        password = '123';
SELECT * FROM mysql(creds, table='test');

┌─int_id─┬─float─┐
│      1 │     2 │
└────────┴───────┘

Replacing and inserting:

INSERT INTO FUNCTION mysql('localhost:3306', 'test', 'test', 'bayonet', '123', 1) (int_id, float) VALUES (1, 3);
INSERT INTO TABLE FUNCTION mysql('localhost:3306', 'test', 'test', 'bayonet', '123', 0, 'UPDATE int_id = int_id + 1') (int_id, float) VALUES (1, 4);
SELECT * FROM mysql('localhost:3306', 'test', 'test', 'bayonet', '123');

┌─int_id─┬─float─┐
│      1 │     3 │
│      2 │     4 │
└────────┴───────┘

Copying data from MySQL table into ClickHouse table:

CREATE TABLE mysql_copy
(
   `id` UInt64,
   `datetime` DateTime('UTC'),
   `description` String,
)
ENGINE = MergeTree
ORDER BY (id,datetime);

INSERT INTO mysql_copy
SELECT * FROM mysql('host:port', 'database', 'table', 'user', 'password');

Or if copying only an incremental batch from MySQL based on the max current id:

INSERT INTO mysql_copy
SELECT * FROM mysql('host:port', 'database', 'table', 'user', 'password')
WHERE id > (SELECT max(id) FROM mysql_copy);

​Syntax

​Arguments

​Returned value

​Examples

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Syntax

Arguments

Returned value

Examples

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