DuckDB MySQL extension

The MySQL extension allows DuckDB to directly read and write data from a MySQL database instance. The data can be queried directly from the underlying MySQL database. Data can be loaded from MySQL tables into DuckDB tables, or vice versa.

Reading Data from MySQL

To make a MySQL database accessible to DuckDB use the ATTACH command:

ATTACH 'host=localhost user=root port=0 database=mysqlscanner' AS mysqlscanner (TYPE mysql_scanner)
USE mysqlscanner;

The connection string determines the parameters for how to connect to MySQL as a set of key=value pairs. Any options not provided are read from the corresponding environment variables if set, and otherwise replaced by their default values, as per the table below.

Setting	Description	Environment Variable	Default
host	Name of host to connect to	MYSQL_HOST	localhost
user	MySQL user name	MYSQL_USER	current_user
password	MySQL password	MYSQL_PWD
database	Database name	MYSQL_DATABASE	NULL
port	Port number	MYSQL_TCP_PORT	0
socket	Unix socket file name	MYSQL_UNIX_PORT	NULL
compress	Compress MySQL packet	MYSQL_COMPRESS	1

The tables in the file can be read as if they were normal DuckDB tables, but the underlying data is read directly from MySQL at query time.

D SHOW TABLES;
┌───────────────────────────────────────┐
│                 name                  │
│                varchar                │
├───────────────────────────────────────┤
│ signed_integers                       │
└───────────────────────────────────────┘
D SELECT * FROM signed_integers;
┌──────┬────────┬──────────┬─────────────┬──────────────────────┐
│  t   │   s    │    m     │      i      │          b           │
│ int8 │ int16  │  int32   │    int32    │        int64         │
├──────┼────────┼──────────┼─────────────┼──────────────────────┤
│ -128 │ -32768 │ -8388608 │ -2147483648 │ -9223372036854775808 │
│  127 │  32767 │  8388607 │  2147483647 │  9223372036854775807 │
│ NULL │   NULL │     NULL │        NULL │                 NULL │
└──────┴────────┴──────────┴─────────────┴──────────────────────┘

It might be desirable to create a copy of the MySQL databases in DuckDB to prevent the system from re-reading the tables from MySQL continuously, particularly for large tables.

Data can be copied over from MySQL to DuckDB using standard SQL, for example:

CREATE TABLE duckdb_table AS FROM mysqlscanner.mysql_table;

Writing Data to MySQL

In addition to reading data from MySQL, create tables, ingest data into MySQL and make other modifications to a MySQL database using standard SQL queries.

This allows you to use DuckDB to, for example, export data that is stored in a MySQL database to Parquet, or read data from a Parquet file into MySQL.

Below is a brief example of how to create a new table in MySQL and load data into it.

ATTACH 'host=localhost user=root port=0 database=mysqlscanner' AS mysql_db (TYPE mysql_scanner);
CREATE TABLE mysql_db.tbl(id INTEGER, name VARCHAR);
INSERT INTO mysql_db.tbl VALUES (42, 'DuckDB');

Many operations on MySQL tables are supported. All these operations directly modify the MySQL database, and the result of subsequent operations can then be read using MySQL. Note that if modifications are not desired, ATTACH can be run with the READ_ONLY property which prevents making modifications to the underlying database. For example:

ATTACH 'host=localhost user=root port=0 database=mysqlscanner' AS mysql_db (TYPE mysql_scanner, READ_ONLY);

Below is a list of supported operations.

CREATE TABLE

CREATE TABLE mysql_db.tbl(id INTEGER, name VARCHAR);

INSERT INTO

INSERT INTO mysql_db.tbl VALUES (42, 'DuckDB');

SELECT

SELECT * FROM mysql_db.tbl;
┌───────┬─────────┐
│  id   │  name   │
│ int64 │ varchar │
├───────┼─────────┤
│    42 │ DuckDB  │
└───────┴─────────┘

COPY

COPY mysql_db.tbl TO 'data.parquet';
COPY mysql_db.tbl FROM 'data.parquet';

UPDATE

UPDATE mysql_db.tbl SET name='Woohoo' WHERE id=42;

DELETE

DELETE FROM mysql_db.tbl WHERE id=42;

ALTER TABLE

ALTER TABLE mysql_db.tbl ADD COLUMN k INTEGER;

DROP TABLE

DROP TABLE mysql_db.tbl;

CREATE VIEW

CREATE VIEW mysql_db.v1 AS SELECT 42;

CREATE SCHEMA/DROP SCHEMA

CREATE SCHEMA mysql_db.s1;
CREATE TABLE mysql_db.s1.integers(i int);
INSERT INTO mysql_db.s1.integers VALUES (42);
SELECT * FROM mysql_db.s1.integers;
┌───────┐
│   i   │
│ int32 │
├───────┤
│    42 │
└───────┘
DROP SCHEMA mysql_db.s1;

Transactions

CREATE TABLE mysql_db.tmp(i INTEGER);
BEGIN;
INSERT INTO mysql_db.tmp VALUES (42);
SELECT * FROM mysql_db.tmp;
┌───────┐
│   i   │
│ int64 │
├───────┤
│    42 │
└───────┘
ROLLBACK;
SELECT * FROM mysql_db.tmp;
┌────────┐
│   i    │
│ int64  │
├────────┤
│ 0 rows │
└────────┘

Note that DDL statements are not transactional in MySQL.

Settings

name	description	default
mysql_experimental_filter_pushdown	Whether or not to use filter pushdown (currently experimental)	false
mysql_tinyint1_as_boolean	Whether or not to convert TINYINT(1) columns to BOOLEAN	true
mysql_debug_show_queries	DEBUG SETTING: print all queries sent to MySQL to stdout	false
mysql_bit1_as_boolean	Whether or not to convert BIT(1) columns to BOOLEAN	true

Schema Cache

To avoid having to continuously fetch schema data from MySQL, DuckDB keeps schema information - such as the names of tables, their columns, etc - cached. If changes are made to the schema through a different connection to the MySQL instance, such as new columns being added to a table, the cached schema information might be outdated. In this case, the function mysql_clear_cache can be executed to clear the internal caches.

CALL mysql_clear_cache();

Development

Dependencies

The package depends on vcpkg, and has several platform-specific dependencies that must be installed in order for compilation to succeed.

Submodules

The DuckDB submodule must be initialized prior to building.

git submodule init
git pull --recurse-submodules

vcpkg

vcpkg must be installed and configured for building. For more information, see here.

git clone https://github.com/Microsoft/vcpkg.git
./vcpkg/bootstrap-vcpkg.sh
export VCPKG_TOOLCHAIN_PATH=`pwd`/vcpkg/scripts/buildsystems/vcpkg.cmake

Ubuntu

sudo apt-get install -y ninja-build cmake build-essential make ccache curl zip unzip tar
sudo apt-get install -y pkg-config autoconf autoconf-archive

MacOS

brew install pkg-config ninja automake autoconf autoconf-archive libevent

Building & Loading the Extension

To build, type:

make

To run, run the bundled duckdb shell:

 ./build/release/duckdb -unsigned

Then, load the MySQL extension like so:

LOAD 'build/release/extension/mysql_scanner/mysql_scanner.duckdb_extension';

Testing

Tests can be run with the following command:

make test

Note that most test will require to have a mysql server running to actually run. To run these tests, setup the mysql server and set the environment variable MYSQL_TEST_DATABASE_AVAILABLE=1.