Mastering PostgreSQL 12 - Third Edition

Step 1: Inlining the view

The first transformation that the optimizer does is inline the views. Here's what happens:

SELECT * FROM (   SELECT *    FROM a, b    WHERE aid = bid) AS v, c WHERE v.aid = c.cid       AND cid = 4;

The view is inlined and transformed into a subselect. What does this one buy us? Actually, nothing. All it does is open the door for further optimization, which will really be a game-changer for this query.