[Solved] Which statement best describes how PostgreSQL executes a correlated subquery? — Ans: It executes the subquery for each row of the outer query using that row's... | PostgreSQL

PostgreSQL - Subqueries in PostgreSQL

Which statement best describes how PostgreSQL executes a correlated subquery?

AIt executes the subquery once and reuses the result for all outer rows.

BIt executes the subquery for each row of the outer query using that row's values.

CIt executes the subquery only if the outer query has no rows.

DIt executes the subquery after the outer query completes.

Step-by-Step Solution

Solution:

Step 1: Identify execution timing of correlated subqueries
Correlated subqueries run once per outer query row, using that row's values.
Step 2: Eliminate incorrect options
Options B, C, and D describe behaviors not matching correlated subqueries.
Final Answer:
It executes the subquery for each row of the outer query using that row's values. -> Option B
Quick Check:
Execution per outer row = It executes the subquery for each row of the outer query using that row's values. [OK]

Quick Trick: Correlated subqueries run repeatedly, once per outer row. [OK]

Common Mistakes:

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Which statement best describes how PostgreSQL executes a correlated subquery?