I like the book, thanks for your hard work.
Many companies do not allow for raw sql execution as it opens the door to sql injection attacks. Instead stored procedures are preferred. That certainly brings its own complexity with syncing the db with the version of code running against it.
I think it is worth mentioning in chapter 4 that stored procedures are not well supported or give a hyperlink to show how people are doing it until there is better support in org.clojure/java.jdbc . I did not find an easy way to execute one besides wrapping some java, but maybe I did not look hard enough.