[curryhoward]

The author makes it crystal clear that she is not advocating this as a mental model for the execution of the query:

Database engines don’t actually literally run queries in this order because they implement a bunch of optimizations to make queries run faster – we’ll get to that a little later in the post.

So:

- you can use this diagram when you just want to understand which queries are valid and how to reason about what results of a given query will be

- you shouldn’t use this diagram to reason about query performance or anything involving indexes, that’s a much more complicated thing with a lot more variables

She claims this is a useful tool to understand the denotational semantics of the query and which kinds of queries are allowed vs. not allowed—and she's absolutely right.