1) inner join has only join, usually inner is omitted
2) left join, right join and full join are outer join, outer is usually omitted.
3) joint table, both ids from two tables will be primary
mysql examples: (typing it down makes me remember it longer)
alter table invoice_items add foreign key (invoice_id) references invoices(invoice_id); //add foreign key
insert food(name, asin) values(‘apple’, ‘1234’)
each INDEX table is identified by the primary id, it stores in a 8k page, either in disk or ram.