How would you find the latest record per group, such as each customer latest order?
Model answer
Use ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY created_at DESC) and keep row 1, or join to a subquery of MAX(created_at) per customer (careful with ties). PostgreSQL also has DISTINCT ON for this.
Learn this topic
SQL JOINs: INNER JOIN and LEFT JOIN Explained in the course SQL for Beginners: Learn Databases Step by Step.
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