Let's say you've set up a fresh new instance of MySQL. Perhaps in a docker container with a MySQL image. When you first connect to the instance, you'll be prompted for a username and password.
What is the username and password for a MySQL instance you've just created?
There are defaults. The default username is root and the default password is
left blank.
So, your connection URL will look something like this:
mysql://root@localhost:3306
You can use that on the CLI or plug it in to the connection details panel of your favorite SQL client.