Multiple column joins

When a join query specifies multiple join columns on two tables, and there is a composite index on the columns, the composite total density is used. For example, if authors and publishers each has an index on city, state, the composite total density for city, state is used for each table in this query:

select au_lname, pub_name
from authors a, publishers p
where a.city = p.city
and a.state = p.state