Hash join example plan

- [Instructor] We're back in pgAdmin now, to see what an explain plan with a hash join looks like. We'll start with the commands that will force the use of the hash join. We'll set enable_nestloop to false and set enable_hashjoin to true, and we'll set enable_mergejoin to false. Now, we'll add the same query we looked at in the nested loop example, and that is SELECT, and from the staff table, we're going to pull the ID, the last name, the job title, and then from the company regions, we're going to get the country. Then it'll be FROM staff. Excuse me, I'll pull that down a little bit. From the staff table, which we'll alias with an s, and we'll INNER JOIN on company_regions, which we'll alias with a cr, and of course, this will be ON region_id in both tables. Okay, let's just make sure I put that in correctly by executing. Okay, we got the data we were expecting, so let's look at the explain plan. Move that up a little bit. Notice, this query uses a hash join as expected. Row 4 in the explain plan indicates the hash table is built on the company regions table. Row 3 indicates we're scanning the staff table and calculating a hash value, which is compared in Row 2. The total cost of this join is just under 24 computational units.