# MySQL connector#

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

## Requirements#

To connect to MySQL, you need:

• MySQL 5.7, 8.0 or higher.

• Network access from the Trino coordinator and workers to MySQL. Port 3306 is the default port.

## 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


The connection-url defines the connection information and parameters to pass to the MySQL JDBC driver. The supported parameters for the URL are available in the MySQL Developer Guide.

For example, the following connection-url allows you to configure the JDBC driver to interpret time values based on UTC as a timezone on the server, and serves as a workaround for a known issue.

connection-url=jdbc:mysql://example.net:3306?serverTimezone=UTC


The connection-user and connection-password are typically required and determine the user credentials for the connection, often a service user. You can use secrets to avoid actual values in the catalog properties files.

### 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, Trino creates a catalog named sales using the configured connector.

### General configuration properties#

The following table describes general catalog configuration properties for the connector:

Property name

Description

Default value

case-insensitive-name-matching

Support case insensitive schema and table names.

false

case-insensitive-name-matching.cache-ttl

1m

case-insensitive-name-matching.config-file

Path to a name mapping configuration file in JSON format that allows Trino to disambiguate between schemas and tables with similar names in different cases.

null

case-insensitive-name-matching.refresh-period

Frequency with which Trino checks the name matching configuration file for changes.

0 (refresh disabled)

metadata.cache-ttl

Duration for which metadata, including table and column statistics, is cached.

0 (caching disabled)

metadata.cache-missing

Cache the fact that metadata, including table and column statistics, is not available

false

metadata.cache-maximum-size

Maximum number of objects stored in the metadata cache

10000

write.batch-size

Maximum number of statements in a batched execution. Do not change this setting from the default. Non-default values may negatively impact performance.

1000

### Procedures#

• system.flush_metadata_cache()

Flush JDBC metadata caches. For example, the following system call flushes the metadata caches for all schemas in the example catalog

USE example.myschema;


#### Case insensitive matching#

When case-insensitive-name-matching is set to true, Trino is able to query non-lowercase schemas and tables by maintaining a mapping of the lowercase name to the actual name in the remote system. However, if two schemas and/or tables have names that differ only in case (such as “customers” and “Customers”) then Trino fails to query them due to ambiguity.

In these cases, use the case-insensitive-name-matching.config-file catalog configuration property to specify a configuration file that maps these remote schemas/tables to their respective Trino schemas/tables:

{
"schemas": [
{
"remote": "CaseSensitiveName",
"mapping": "case_insensitive_1"
},
{
"remote": "cASEsENSITIVEnAME",
"mapping": "case_insensitive_2"
}],
"tables": [
{
"remoteSchema": "CaseSensitiveName",
"remoteTable": "tablex",
"mapping": "table_1"
},
{
"remoteSchema": "CaseSensitiveName",
"remoteTable": "TABLEX",
"mapping": "table_2"
}]
}


Queries against one of the tables or schemes defined in the mapping attributes are run against the corresponding remote entity. For example, a query against tables in the case_insensitive_1 schema is forwarded to the CaseSensitiveName schema and a query against case_insensitive_2 is forwarded to the cASEsENSITIVEnAME schema.

At the table mapping level, a query on case_insensitive_1.table_1 as configured above is forwarded to CaseSensitiveName.tablex, and a query on case_insensitive_1.table_2 is forwarded to CaseSensitiveName.TABLEX.

By default, when a change is made to the mapping configuration file, Trino must be restarted to load the changes. Optionally, you can set the case-insensitive-name-mapping.refresh-period to have Trino refresh the properties without requiring a restart:

case-insensitive-name-mapping.refresh-period=30s


### Non-transactional INSERT#

The connector supports adding rows using INSERT statements. By default, data insertion is performed by writing data to a temporary table. You can skip this step to improve performance and write directly to the target table. Set the insert.non-transactional-insert.enabled catalog property or the corresponding non_transactional_insert catalog session property to true.

Note that with this property enabled, data can be corrupted in rare cases where exceptions occur during the insert operation. With transactions disabled, no rollback can be performed.

## Type mapping#

Because Trino and MySQL each support types that the other does not, this connector modifies some types when reading or writing data.

### MySQL to Trino read type mapping#

This connector supports reading the following MySQL types and performs conversion to Trino types with the detailed mappings as shown in the following table.

MySQL to Trino type mapping#

MySQL database type

Trino type

Notes

BIT

BOOLEAN

BOOLEAN

TINYINT

TINYINT

TINYINT

SMALLINT

SMALLINT

INTEGER

INTEGER

BIGINT

BIGINT

DOUBLE PRECISION

DOUBLE

FLOAT

REAL

REAL

REAL

DECIMAL(p, s)

DECIMAL(p, s)

CHAR(n)

CHAR(n)

VARCHAR(n)

VARCHAR(n)

TINYTEXT

VARCHAR(255)

TEXT

VARCHAR(65535)

MEDIUMTEXT

VARCHAR(16777215)

LONGTEXT

VARCHAR

BINARY, VARBINARY, TINYBLOB, BLOB, MEDIUMBLOB, LONGBLOB

VARBINARY

DATE

DATE

TIME(n)

TIME(n)

DATETIME(n)

DATETIME(n)

TIMESTAMP(n)

TIMESTAMP(n)

No other types are supported.

### Trino to MySQL write type mapping#

This connector supports writing the following Trino types and performs conversion to MySQL types with the detailed mappings as shown in the following table.

Trino to MySQL type mapping#

Trino type

MySQL type

Notes

BOOLEAN

TINYINT

TINYINT

TINYINT

SMALLINT

SMALLINT

INTEGER

INTEGER

BIGINT

BIGINT

REAL

REAL

DOUBLE

DOUBLE PRECISION

DECIMAL(p, s)

DECIMAL(p, s)

MySQL DECIMAL type handling

CHAR(n)

CHAR(n)

VARCHAR(n)

VARCHAR(n)

DATE

DATE

TIME(n)

TIME(n)

TIMESTAMP(n)

TIMESTAMP(n)

No other types are supported.

### Decimal type handling#

DECIMAL types with precision larger than 38 can be mapped to a Trino DECIMAL by setting the decimal-mapping configuration property or the decimal_mapping session property to allow_overflow. The scale of the resulting type is controlled via the decimal-default-scale configuration property or the decimal-rounding-mode session property. The precision is always 38.

By default, values that require rounding or truncation to fit will cause a failure at runtime. This behavior is controlled via the decimal-rounding-mode configuration property or the decimal_rounding_mode session property, which can be set to UNNECESSARY (the default), UP, DOWN, CEILING, FLOOR, HALF_UP, HALF_DOWN, or HALF_EVEN (see RoundingMode).

### General configuration properties#

The following properties can be used to configure how data types from the connected data source are mapped to Trino data types and how the metadata is cached in Trino.

Property name

Description

Default value

unsupported-type-handling

Configure how unsupported column data types are handled:

• IGNORE, column is not accessible.

• CONVERT_TO_VARCHAR, column is converted to unbounded VARCHAR.

The respective catalog session property is unsupported_type_handling.

IGNORE

jdbc-types-mapped-to-varchar

Allow forced mapping of comma separated lists of data types to convert to unbounded VARCHAR

## 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.

## Pushdown#

The connector supports pushdown for a number of operations:

Aggregate pushdown for the following functions:

### Predicate pushdown support#

The connector does not support pushdown of any predicates on columns with textual types like CHAR or VARCHAR. This ensures correctness of results since the data source may compare strings case-insensitively.

In the following example, the predicate is not pushed down for either query since name is a column of type VARCHAR:

SELECT * FROM nation WHERE name > 'CANADA';
SELECT * FROM nation WHERE name = 'CANADA';


## SQL support#

If a WHERE clause is specified, the DELETE operation only works if the predicate in the clause can be fully pushed down to the data source.