The Difference Between Subquery and Correlated Subquery in Oracle SQL

In Oracle SQL, the main difference between a subquery and a correlated subquery lies in their relationship with the outer query.

Subquery:

A subquery, also known as a nested query or inner query, is a query nested within another query. It is independent of the outer query and is executed first before the outer query. The result of the subquery is then used by the outer query to perform further actions.

Correlated Subquery:

A correlated subquery, on the other hand, is a type of subquery where the inner query references a column from the outer query. This creates a relationship between the inner and outer queries, with the inner query being re-executed for each row processed by the outer query. This can impact performance but provides the ability to evaluate conditions based on the outer query's data.

Overall, understanding the distinction between subquery and correlated subquery is essential for optimizing SQL queries in Oracle databases.