To do this first locate config folder in your root. Then open connections.js
Locate
  // someMysqlServer: {
  //   adapter: 'sails-mysql',
  //   host: 'YOUR_MYSQL_SERVER_HOSTNAME_OR_IP_ADDRESS',
  //   user: 'YOUR_MYSQL_USER', //optional
  //   password: 'YOUR_MYSQL_PASSWORD', //optional
  //   database: 'YOUR_MYSQL_DB' //optional
  // },
Uncomment these lines.
Give suitable name for the connector like this someMysqlServer to mysql_connection or any name as your wish
  mysql_connection: {
    adapter: 'sails-mysql',
    host: '127.0.0.1', // can user localhost or mysql connection either
    user: 'root', // your mysql username
    password: 'xxxxxxxxx', // your mysql password
    database: 'your database name here' // database name
  },
Save file
Go to your root folder and run following command :
$ npm install sails-mysql --save
Note: by running above command we are installing mysql driver package for sails.js.
Your are done.
Now you can use mysql_connection as connection name in your model config. When you lift your app using following command:
$ sails lift
you model schema will automatically get updated in MySQL database