So i have to deal with the following scenario:
I have a table , users , which holds all of the users of my application . Each user has an email which is unique and thus could be the primary key of said table .
Let's now say i have a second table that associates some data with a user . What pops into my mind is to have that second table hold an email column which i can then use to associate a row with a user .Is this approach bad in terms of memory? Will MySQL store said email repeatedly for each extra table that holds an email column to reference users table? Should i instead just use an auto-increment id for each user and use that for the whole reference thing since an integer is way lighter than a string big enough to hold an email?