Every now and then you might encounter a situation where you need to have a database column that has a value based on a formula consisting of values of other columns. Unfortunately, there is no standard way of embedding this into the SQL definition of a table. You must keep track of updating this value on your own when using the database.
But, this begs the question, why would I want to have a formula field? Can’t I just do all my calculations when I am fetching my data with a SQL query? Sure, you can. However, if you are doing calculations on vast amounts of data, having part of this data pre-calculated in a formula field can give you a solid performance boost.
If you’re using Ruby on Rails for your project, there’s a very simple solution you can implement. I’ll show you how through a trivial example. In this example, we imagine a teacher wanting to store his students’ assignment marks.
Let’s go ahead and create our rails project called teacherexample. I’ll use MySQL as my database in this example, but the concept applies to any database system.