Netflix-style SQL interview exerciseMediumVerified answerSQLite live

Sci-Fi Viewers

Return distinct user_id values for all users who have watched at least one Sci-Fi movie, ordered by user_id.

  • Joins
  • Filtering
  • Sorting
  • Distinct values

Interview brief

Understand the request

Recommendations — Sci-Fi Cluster The recommendations team is building a Sci-Fi affinity segment to test a targeted content push.

Return distinct Sci-Fi viewer IDs and order the result by user ID.

Return

  • user_id

Constraints

  • Return identified users who watched at least one 'Sci-Fi' movie
  • Return each user once
  • Order by user ID

Data you will use

Review the relevant tables before deciding how to join, filter, or aggregate them.

watch_history

  • user_idINTEGER
  • movie_idINTEGER

movies

  • movie_idINTEGER
  • genreVARCHAR(50)

Hints, when you need them

Open one clue at a time so you still do the reasoning.

Hint 1

Connect watch facts to catalog genres through movie ID.

Hint 2

Filter the genre and deduplicate identified viewers.

Hint 3

Return viewer IDs in stable order.

Verified SQL answer

Attempt the problem first, then compare structure and reasoning—not just syntax.

Reveal solution and explanation
SELECT DISTINCT w.user_id FROM watch_history w INNER JOIN movies m ON w.movie_id = m.movie_id WHERE w.user_id IS NOT NULL AND m.genre = 'Sci-Fi' ORDER BY w.user_id

Why this works

Joining watch_history to movies links each viewing session to its genre. WHERE genre = 'Sci-Fi' keeps only Sci-Fi sessions. DISTINCT prevents a user appearing twice if they watched multiple Sci-Fi titles.

Success check

Returns the complete deterministic result for sci-fi viewers

Expected result

Use this output to verify values, aliases, ordering, and row count.

user_id
1
2
5
6
8

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