12.16. MySQL Connector

The MySQL connector allows querying and creating tables in an external MySQL database. This can be used to join data between different systems like MySQL and Hive, or between two different MySQL instances.

Configuration

To configure the MySQL connector, create a catalog properties file in etc/catalog named, for example, mysql.properties, to mount the MySQL connector as the mysql catalog. Create the file with the following contents, replacing the connection properties as appropriate for your setup:

connector.name=mysql
connection-url=jdbc:mysql://example.net:3306
connection-user=root
connection-password=secret

Multiple MySQL Servers

You can have as many catalogs as you need, so if you have additional MySQL servers, simply add another properties file to etc/catalog with a different name (making sure it ends in .properties). For example, if you name the property file sales.properties, Presto will create a catalog named sales using the configured connector.

Querying MySQL

The MySQL connector provides a schema for every MySQL database. You can see the available MySQL databases by running SHOW SCHEMAS:

SHOW SCHEMAS FROM mysql;

If you have a MySQL database named web, you can view the tables in this database by running SHOW TABLES:

SHOW TABLES FROM mysql.web;

You can see a list of the columns in the clicks table in the web database using either of the following:

DESCRIBE mysql.web.clicks;
SHOW COLUMNS FROM mysql.web.clicks;

Finally, you can access the clicks table in the web database:

SELECT * FROM mysql.web.clicks;

If you used a different name for your catalog properties file, use that catalog name instead of mysql in the above examples.

Table Statistics

MySQL connector supports table and column statistics. The table-level statistics are based on MySQL’s INFORMATION_SCHEMA.TABLES table. The column-level statistics are based on MySQL’s index statistics INFORMATION_SCHEMA.STATISTICS table. The connector can return column-level statistics only when the column is the first column in some index.

MySQL Database can automatically update its table and index statistics. In some cases, you may want to force statistics update (e.g. after creating new index or after changing data in the table). You can do that by executing the following statement in MySQL Database.

ANALYZE TABLE table_name;

The table and column statistics can be viewed in Presto using SHOW STATS and are used for Cost based optimizations.

Note

MySQL and Presto may use statistics information in different ways. For this reason, the accuracy of table and column statistics returned by the MySQL connector might be lower than than that of others connectors.

Improving Statistics Accuracy

You can improve statistics accuracy with histogram statistics (available since MySQL 8.0). To create histogram statistics execute the following statement in MySQL Database.

ANALYZE TABLE table_name UPDATE HISTOGRAM ON column_name1, column_name2, ...;

Please refer to MySQL documentation for information about options, limitations and additional considerations.

Table Statistics Configuration Properties

Property Name Description Default
statistics.enabled Enables table and column statistics. true
statistics.cache-ttl Duration for which table and column statistics are cached. 0s
statistics.cache-missing Cache the fact that table statistics were not available. false

MySQL Connector Limitations

The following SQL statements are not yet supported: