MySql calculate average grade

Question

I am using MySql and have 2 tables.

What I need is an average grade of all reviews of that organizations. My question is, should I make a trigger and a procedure to allways update average grade on insert or just calculate it when needed? I am going to need it multiple (5-10) times on each page.

Answer 1

A general rule of thumb: Premature optimization are the mother of all evil. Start with calculating the average whenever you need it. If that becomes too slow, you can start thinking about optimizations such as caching it or pre-calculating it and saving it to the database (eg, by a trigger, like you proposed).