A lesson may be canceled, moved to an other time, and possibly switched to an other teacher.
In other words, we have
lessonid INT UNSIGNED canceled BIT(1) time TIME teacherid INT UNSIGNED
Should all these "lesson modifications" be stored in one table? Or one table for canceled and another for moved lessons?
I am inclined to store it into one table (with possibly NULL time and probably NULL
teacherid, because I can add a common "modification ID" (the primary ID of the table) for both cancellations a moves to an other time. But I am open to hear arguments pro and contra.