Google-style Company ChallengeMediumVerified answerSQLite live

Users with Ad Clicks

Which users have clicked on at least one ad?

  • Sorting
  • Distinct values

Challenge brief

Understand the request

Ads Operations needs a deduplicated list of all users who have engaged with at least one advertisement for retargeting purposes.

Return user_id in the declared deterministic order.

Return

  • user_id

Constraints

  • Return each user with an ad click once
  • Order by user ID

Data you will use

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

ad_clicks

  • click_idINTEGER
  • user_idINTEGER
  • ad_idINTEGER
  • click_dateDATE
  • revenueREAL

Hints, when you need them

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

Hint 1

A user may have several click records.

Hint 2

Project the user key only once across the fact table.

Hint 3

Sort the deduplicated identifiers.

Verified SQL answer

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

Reveal solution and explanation
SELECT DISTINCT user_id FROM ad_clicks ORDER BY user_id

Why this works

There are 30 ad click rows but only 20 distinct users. Some users clicked multiple ads (user 1 clicked 4 times, user 4 clicked twice). DISTINCT collapses multiple clicks by the same user into one row.

Success check

Returns the complete deterministic result for users with ad clicks

Expected result

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

user_id
1
2
3
4
5
6
7
8
9
10

Previewing 10 of 21 expected rows. Run the query in the editor to inspect the full result.

Learn the concepts behind this answer

Strengthen your understanding with these targeted learning topics:

Continue practicing

Explore related company challenges

SQL Interview Practice →

Return to the complete interview preparation experience.