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What is a subquery and what is a correlated subquery?

Q: What is a subquery and what is a correlated subquery?

A **subquery** is a query nested inside another. A **correlated subquery** references columns from the outer query, so it's re-evaluated for each outer row — powerful but potentially slow; often rewritable as a join for performance.

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A subquery is a query nested inside another. A correlated subquery references columns from the outer query, so it's re-evaluated for each outer row — powerful but potentially slow; often rewritable as a join for performance.

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