alleryStart learning →A correlated subquery differs from an uncorrelated one in that
Ait always returns exactly one row
Binner uses outer columns; re-runs per outer row
Cit cannot be used inside WHERE clauses
Dit is forbidden in standard SQL
Answer & Solution
Correct answer: B. inner uses outer columns; re-runs per outer row
A correlated subquery uses values from the outer row in its own predicate, so it must be re-evaluated for each outer row.
An uncorrelated subquery can be evaluated once and cached.
Correlated subqueries are slower per row but more expressive
they are fully standard SQL.
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