README.md

How to use MySQL with Deno

MySQL is the most popular database in the 2022 Stack Overflow Developer Survey and counts Facebook, Twitter, YouTube, and Netflix among its users.

You can manipulate and query a MySQL database with Deno using the mysql2 node package and the npm: modifier. This allows us to use its Promise wrapper and take advantage of top-level await.

import mysql from "npm:mysql2/promise";

Connecting to MySQL

We can connect to our MySQL server using the createConnection() method. You need the host (’localhost’ if you are testing, or more likely a cloud database endpoint in production) and the user and password:

const connection = await mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "password",
});

You can also optionally specify a database during the connection creation. Here we are going to use mysql2 to create the database on the fly.

Creating and populating the database

Now that you have the connection running, you can use connection.query() with SQL commands to create databases and tables as well as insert the initial data.

First we want to generate and select the database to use:

await connection.query("CREATE DATABASE denos");
await connection.query("use denos");

Then we want to create the table:

await connection.query(
  "CREATE TABLE `dinosaurs` (   `id` int NOT NULL AUTO_INCREMENT PRIMARY KEY,   `name` varchar(255) NOT NULL,   `description` varchar(255) )"
);

After the table is created we can populate the data:

await connection.query(
  "INSERT INTO `dinosaurs` (id, name, description) VALUES (1, 'Aardonyx', 'An early stage in the evolution of sauropods.'), (2, 'Abelisaurus', 'Abels lizard has been reconstructed from a single skull.'), (3, 'Deno', 'The fastest dinosaur that ever lived.')"
);

We now have all the data ready to start querying.

Querying MySQL

We can use the same connection.query() method to write our queries. First we try and get all the data in our ‘dinosaurs’ table:

const results = await connection.query("SELECT * FROM `dinosaurs`");
console.log(results);

The result from this query is all the data in our database:

[
  [
    {
      id: 1,
      name: "Aardonyx",
      description: "An early stage in the evolution of sauropods."
    },
    {
      id: 2,
      name: "Abelisaurus",
      description: `Abel's lizard" has been reconstructed from a single skull.`
    },
    { id: 3, name: "Deno", description: "The fastest dinosaur that ever lived." }
  ],

If we want to just get a single element from the database, we can change our query:

const [results, fields] = await connection.query(
  "SELECT * FROM `dinosaurs` WHERE `name` = 'Deno'"
);
console.log(results);

Which gives us a single row result:

[{ id: 3, name: "Deno", description: "The fastest dinosaur that ever lived." }];

Finally, we can close the connection:

await connection.end();

For more on mysql2 you can check out their documentation here.