On page 120,
Due to the slight formatting errata already noted on this page, those of us (like me) who actually executed mix ecto.migrate at this stage created a table that did not enforce the unique index constraint that the next chapter talks about. This caused some confusion and required me to have to look up how to check on the table and index directly in postgres in order to locate the problem. Of course this is a simply issues for someone already familiar with postgres or phoenix, but given that I am learning both at the same time while following along in this book, it was confusing to track down the problem. (was it the migration that is the problem? was it because I’m using a newer version of phoenix from the book?)

I think a short line right above the “Next, let’s edit our migration to market the name field as NOT NULL and create a unique index for it:” saying
“make sure not to execute mix ecto.migrate just yet”
would have made it clear that we want to change the migration generated files before we actually create the table in the db.