🔗 Why are database columns 191 characters?

Sometimes, when you are looking at a database’s schema, you see that there are text fields defined like this:

email_address varchar(191) NOT NULL

This means that the column supports strings with a maximum length of 191 characters, and can’t be null. 191 is such an odd number - where did it come from? In this post, we’ll look at the historical reasons for the 191 character limit as a default in most relational databases.