Mastering PostgreSQL 10

Applying transformations

Obviously, doing the obvious thing (joining the view first) makes no sense at all. A nested loop would send execution times through the roof. A hash join has to hash millions of rows and a nested loop has to sort 300 million rows. All three options are clearly unsuitable here. The way out is to apply logical transformations to make the query fast. In this section, you will learn what the planner does to speed up the query. A couple of steps will be performed.