In previous chapters, we learned how to execute SQL queries. We started by writing simple queries, then moved on to writing more complex queries; we learned how to use aggregates in the traditional way, and in Chapter 5, Advanced Statements, we talked about window functions, which are another way to write aggregates. In this chapter, we will add server-side programming to this list of skills. Server-side programming can be useful in many cases as it moves the programming logic from the client side to the database side. For example, we could use it to take a function that has been written many times at different points of the application program and move it inside the server so that it is written only once, meaning that in case of modification, we only have to modify one function. In this chapter, we will also look at how PostgreSQL can manage different...