Challenging: Store and Query Music Lesson Management System

I am about to begin development on a website which manages the availability of a cello teacher and lessons that students have signed up for. Currently, I have two tables: Availability (date, startTime, endTime) - This table stores time spans that people can sign up for lessons Lessons (date

I want LEFT JOIN to return NULL if WHERE not matched

Two tables, groups and user_permissions. Groups is indexed by groupid as primary key. User_permissions is indexed by username and groupid. For each user that's in a group, a row in user_permissions exists. I want to select from groups and user_permissions looking for a certain user in user_pe