MySQL MembershipProvider in Umbraco 7
If you want to use a custom MembershipProvider for Umbraco instead of the built in here is how I managed to connect to a MySQL database, create tables in that database automatically and query the database from Umbraco/C# while the rest of Umbraco uses a SQL databse. You should note that installing a custom MembershipProvider will leave the member section in Umbraco useless.
Preparation
I already had a WAMP stack installed (AMPPS) so I started by starting up the MySQL and through phpMyAdmin I created a new database to store the members.