Crucial Exams

AWS Certified Data Engineer Associate DEA-C01 Practice Question

An ecommerce company stores clickstream events in an Amazon Redshift table named events with columns (session_id VARCHAR, event_ts TIMESTAMP, page VARCHAR). To build a downstream table that contains only the earliest page visited in each session, the engineer wants to write a single SQL statement that avoids self-joins or subqueries. Which query pattern meets these requirements while scanning the table only once?

  • SELECT DISTINCT session_id, FIRST_VALUE(page) OVER (PARTITION BY session_id ORDER BY event_ts) AS page FROM events;

  • SELECT e.session_id, e.page FROM events e INNER JOIN (SELECT session_id, MIN(event_ts) AS first_ts FROM events GROUP BY session_id) s ON e.session_id = s.session_id AND e.event_ts = s.first_ts;

  • SELECT session_id, page FROM events ORDER BY event_ts LIMIT 1;

  • SELECT session_id, page FROM events QUALIFY ROW_NUMBER() OVER (PARTITION BY session_id ORDER BY event_ts) = 1;

AWS Certified Data Engineer Associate DEA-C01
Data Ingestion and Transformation
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