Understanding Subquery vs Correlated Subquery in Oracle SQL

When it comes to writing queries in Oracle SQL, it's essential to grasp the distinctions between a subquery and a correlated subquery. Let's delve into the differences:

Subquery

A subquery, also known as an inner query or nested query, is a query nested within another SQL query. It's self-contained and can run independently of the outer query. The result of a subquery is used by the outer query to further filter or manipulate the data.

Correlated Subquery

A correlated subquery, on the other hand, is a subquery that depends on the outer query for its execution. Unlike a standard subquery, a correlated subquery is executed repeatedly for each row processed by the outer query. This means that the inner query is evaluated in conjunction with the outer query.

Therefore, the main difference lies in the dependency: a subquery is autonomous, while a correlated subquery is interdependent with the outer query.

Understanding the nuances between subqueries and correlated subqueries in Oracle SQL is crucial for optimizing query performance and achieving the desired results.

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