Node name: NLJOIN
Represents: A nested loop join that scans (usually with an index scan) the inner table once for each row of the outer table.
A join is necessary whenever there is more than one table referenced in a FROM clause. A nested loop join does not require a join predicate, but generally performs better with one.
Another (less important) way to make the join more efficient is to create an index on the join columns of the outer table so that the outer table is ordered.