Imagine we have three tables in a MySQL database:

* posts
* categories
* category\_post

There is a one-to-many relationship between **posts** and **categories** so that a single post may have many categories.

The **category\_post** table is the pivot table between **categories** and **posts** and has the following columns:

* id (primary key, auto-incrementing, big integer)
* category\_id
* post\_id

Let's also imagine that we have 1,000,000 rows in our **category\_post** table.

My question is:

Is there any performance benefit to having the **id** column in the **category\_post** table or does it just take up extra space?