CREATE STATISTICS is definitely one of my personal favorite features of PostgreSQL 10.0 because it allows consultants to help customers in many real-world situations. So, what is it all about? When you run SQL, the optimizer has to come up with clever decisions to speed up your queries. However, to do so, it has to rely heavily on estimates to figure out how much data a certain clause or a certain operation returns. Before version 10.0, PostgreSQL only had information about individual columns. Let's look at an example:
SELECT * FROM car WHERE vendor = 'Ford' AND model = 'Mini Clubman';
In version 9.6, PostgreSQL checks which fraction of the table matches Ford and which fraction matches Mini Clubman. Then, ...
