[Solved] Which of these is a valid use case for a LATERAL join? — Ans: Selecting the top 3 orders per customer using a subquery | PostgreSQL

PostgreSQL - Joins in PostgreSQL

Which of these is a valid use case for a LATERAL join?

ASelecting the top 3 orders per customer using a subquery

BJoining two tables without any condition

CCreating a view without any parameters

DUpdating multiple tables in one statement

Step-by-Step Solution

Solution:

Step 1: Identify typical LATERAL use cases
LATERAL is often used to run a subquery per row of a preceding table, like selecting top N related rows.
Step 2: Match options to use cases
Selecting the top 3 orders per customer using a subquery matches this perfectly: top 3 orders per customer needs a subquery per customer row.
Final Answer:
Selecting the top 3 orders per customer using a subquery -> Option A
Quick Check:
LATERAL use case = per-row subquery like top N rows [OK]

Quick Trick: Use LATERAL for per-row subqueries like top N items [OK]

Common Mistakes:

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Which of these is a valid use case for a LATERAL join?