MySQL 8 Administrator???s Guide

Shortening up primary keys

Small is good for primary keys too. Shortening up primary keys would benefit analogously to how we discussed datatypes. Because of smaller primary keys, your index size would be smaller and hence the usage of cache would be less, so it can accommodate more data in memory.

It is preferred to use numeric types, as these would be much smaller than characters to achieve the goal of shortening up primary keys. It can be helpful while doing joins, as generally, primary keys are referred for the joining.