what are correlated and non correlated subquery
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what are correlated and non correlated subquery

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Noncorrelated Subqueries
A noncorrelated subquery executes independently of the outer query. The subquery executes first, and then passes its results to the outer query, For example:

=> SELECT name, street, city, state FROM addresses WHERE state IN (SELECT state FROM states);

Correlated Subqueries
A correlated subquery typically obtains values from its outer query before it executes. When the subquery returns, it passes its results to the outer query.

=> SELECT name, street, city, state FROM addresses
     WHERE EXISTS (SELECT * FROM states WHERE states.state = addresses.state);