what are correlated and non correlated subquery

1Noncorrelated Subqueries
2A noncorrelated subquery executes independently of the outer query. The subquery executes first, and then passes its results to the outer query, For example:
3
4=> SELECT name, street, city, state FROM addresses WHERE state IN (SELECT state FROM states);
5
6Correlated Subqueries
7A correlated subquery typically obtains values from its outer query before it executes. When the subquery returns, it passes its results to the outer query.
8
9=> SELECT name, street, city, state FROM addresses
10     WHERE EXISTS (SELECT * FROM states WHERE states.state = addresses.state);