This chapter described the advanced SQL concepts and features like common table expressions and window functions. These features allow implementing a logic that would not be possible without them, that is, recursive queries.

The other techniques explained here, like the DISTINCT ON clause, the FILTER clause or lateral subqueries, are not that irreplaceable. But they can help in making a query smaller, easier, and faster.

SQL can be used to implement a very complicated logic. However, in difficult cases, the queries can become overcomplicated and very hard to maintain. Moreover, sometimes it is not possible to do some things in pure SQL. In those cases, one needs a procedural language to implement an algorithm. The next chapter will introduce one of them: PL/pgSQL.