ClickHouse/docs/en/engines/database-engines/mysql.md

toc_priority	toc_title
30	MySQL

MySQL

Allows to connect to databases on a remote MySQL server and perform INSERT and SELECT queries to exchange data between ClickHouse and MySQL.

The MySQL database engine translate queries to the MySQL server so you can perform operations such as SHOW TABLES or SHOW CREATE TABLE.

You cannot perform the following queries:

• RENAME
• CREATE TABLE
• ALTER

Creating a Database

CREATE DATABASE [IF NOT EXISTS] db_name [ON CLUSTER cluster]
ENGINE = MySQL('host:port', ['database' | database], 'user', 'password')

Engine Parameters

• host:port — MySQL server address.
• database — Remote database name.
• user — MySQL user.
• password — User password.

Data Types Support

MySQL	ClickHouse
UNSIGNED TINYINT	UInt8
TINYINT	Int8
UNSIGNED SMALLINT	UInt16
SMALLINT	Int16
UNSIGNED INT, UNSIGNED MEDIUMINT	UInt32
INT, MEDIUMINT	Int32
UNSIGNED BIGINT	UInt64
BIGINT	Int64
FLOAT	Float32
DOUBLE	Float64
DATE	Date
DATETIME, TIMESTAMP	DateTime
BINARY	FixedString

All other MySQL data types are converted into String.

Because of the ClickHouse date type has a different range from the MySQL date range,If the MySQL date type is out of the range of ClickHouse date, you can use the setting mysql_datatypes_support_level to modify the mapping from the MySQL date type to the Clickhouse date type: date2Date32 (convert MySQL's date type to ClickHouse Date32) or date2String(convert MySQL's date type to ClickHouse String,this is usually used when your mysql data is less than 1925) or default(convert MySQL's date type to ClickHouse Date).

Nullable is supported.

Global Variables Support

For better compatibility you may address global variables in MySQL style, as @@identifier.

These variables are supported:

• version
• max_allowed_packet

!!! warning "Warning" By now these variables are stubs and don't correspond to anything.

Example:

SELECT @@version;

Examples of Use

Table in MySQL:

mysql> USE test;
Database changed

mysql> CREATE TABLE `mysql_table` (
    ->   `int_id` INT NOT NULL AUTO_INCREMENT,
    ->   `float` FLOAT NOT NULL,
    ->   PRIMARY KEY (`int_id`));
Query OK, 0 rows affected (0,09 sec)

mysql> insert into mysql_table (`int_id`, `float`) VALUES (1,2);
Query OK, 1 row affected (0,00 sec)

mysql> select * from mysql_table;
+------+-----+
| int_id | value |
+------+-----+
|      1 |     2 |
+------+-----+
1 row in set (0,00 sec)

Database in ClickHouse, exchanging data with the MySQL server:

CREATE DATABASE mysql_db ENGINE = MySQL('localhost:3306', 'test', 'my_user', 'user_password')

SHOW DATABASES

┌─name─────┐
│ default  │
│ mysql_db │
│ system   │
└──────────┘

SHOW TABLES FROM mysql_db

┌─name─────────┐
│  mysql_table │
└──────────────┘

SELECT * FROM mysql_db.mysql_table

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

INSERT INTO mysql_db.mysql_table VALUES (3,4)

SELECT * FROM mysql_db.mysql_table

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

Original article