How can you combine LATERAL joins with aggregate functions to find the average order amount per customer, including customers with no orders?

hard📝 Application Q9 of 15

PostgreSQL - Joins in PostgreSQL

How can you combine LATERAL joins with aggregate functions to find the average order amount per customer, including customers with no orders?

AUse INNER JOIN LATERAL with orders grouped by customer

BUse LEFT JOIN LATERAL with a subquery that aggregates orders per customer

CUse CROSS JOIN LATERAL without aggregation

DUse a subquery in SELECT without LATERAL

Step-by-Step Solution

Solution:

Step 1: Include customers with no orders
LEFT JOIN ensures all customers appear even if no matching orders.
Step 2: Use LATERAL with aggregation
The subquery aggregates orders per customer to calculate average amount.
Final Answer:
Use LEFT JOIN LATERAL with a subquery that aggregates orders per customer -> Option B
Quick Check:
LEFT JOIN LATERAL + aggregation = include all with averages [OK]

Quick Trick: LEFT JOIN LATERAL with aggregate subquery includes all rows [OK]

Common Mistakes:

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