I love this guide and will probably steal ideas from it when writing my own SQL tutorials. That said, I don't think SQL is that hard to read compared to other computer languages, at least for non-programmers.

I say this as someone who learned object-oriented programming far before I learned about SQL or its declarative model. SQL was "hard" for me because the declarative style is so functionally different than OOP, and to this day I still haven't ventured to figure out the SQL equivalents of functions, variables, and other mainstays of general programming; I'm satisfied with using a scripting glue language like Python to automate simple SQL SELECT statements.

But I love teaching SQL to non-programmers. You can do a lot of important real-world things with it without having to jump deep into the logical puzzles of "regular" programming. By "deep", I mean things like for-loops; it never fails to surprise me how befuddled beginners are about how for-loops work -- not just the syntax, but the concept of a "block" of code, that for-loops can exist inside of for-loops...or more fundamentally, you can run more than one line of code inside a for-loop.

With SQL, you don't have to worry about any of that. You simply declare what columns you want from a table, what values to filter by, and optionally, how to aggregate it or join it with another table -- concepts that have much clearer analogies to everyday thinking about information (or, at least spreadsheets).

SQL gets complicated when you try to do complicated things. In the OP's opening query, there's a joining of three tables. But without reading it closely, I can already kind of describe the real-world information-need that it fulfills: List the people who have borrowed books that have been borrowed something something to do with `stock`. If I spent a few more minutes, I could figure out what the fuck that subquery, `stock > (SELECT avg(stock) FROM books)` is all about, but the difficulty there is just my ignorance of the domain and/or particular conventions in this hypothetical problem. If I, or even the average novice, wrote this query line-by-line, its purpose would not be so opaque (as writings rarely are to their own authors). The point is that it's much easier for a beginner to author their own SQL without fucking things up in the way you can easily do so with even just a for-loop. I can't imagine that the Python or Ruby equivalent would be nearly as clear as this SQL statement, even for a far simpler kind of join.

My main complaint about SQL is that it seems more logical that the `FROM` clause should come before the `SELECT` statement. Though my initial guess is that that hampers the declarative-clarity of the statement when `JOINS` are involved.

edit: If I could make one suggestion to the submitted article, it would be that the first "Simple Query" is not simple at all:

SELECT bookid AS "id", title
FROM books
WHERE author='Dan Brown';

I'd argue that this is a simpler statement, and one in which the results are immediately recognizable to every spreadsheet user:

SELECT * FROM books;

The default behavior of Excel is to show all columns of a data file. When you get more advanced as a SQL user (and more advanced in understanding the fundamentals of computation), then you start being selective about SELECT and realizing that, as an end user (nevermind the cost of computation), it's not always ideal to see everything by default:

SELECT title FROM books;