Please move this post if it is the wrong section.
I just grabbed a copy of SQL the hard way and clicked around in the online version of the book to get an overview of what’s to come. The link to 2 Introduction in the Contents->Table Of Contents navigation pane points to the wrong page (https://shop.learncodethehardway.org/paid/sql/intro.html). The landing page for the book, which also contains a TOC, contains the correct link: (https://shop.learncodethehardway.org/paid/sql/introduction.html).