Users with Most Reviews
Find users who have written the most reviews.
The challenge runs on the SQLabHub practice database (SQLite) and uses the reviews table. You can solve it in the browser, with nothing to install.
The task
Find users who have written the most reviews.
A correct answer returns 104 rows with 2 columns: user_id, review_count.
Tables used in this challenge
reviews 180 rows
id INTEGER (PK) · product_id INTEGER · user_id INTEGER · rating INTEGER · comment TEXT · reviewed_at TEXT · helpful_votes INTEGER
| id | product_id | user_id | rating | comment | reviewed_at | helpful_votes |
|---|---|---|---|---|---|---|
The first rows of each table are shown. See how all the tables relate on the database schema page.
Expected output
| user_id | review_count |
|---|---|
First 5 of 104 rows. This is the output of the model solution on the practice database.
What you practise
- Summarising many rows into one value with COUNT, SUM, AVG, MIN or MAX
- Grouping rows with GROUP BY to get one result row per group
- Sorting the result with ORDER BY
Hint and approach
Try the challenge first. Open these only when you need them.
Show the hint
GROUP BY user_id ORDER BY COUNT DESC
Show the step-by-step approach
How the model solution is built, in the order the database evaluates it:
- Read from the
reviewstable. - Group the rows by
user_id, so the result has one row for each value. - For each group, compute
COUNT(*). - Sort the result by
review_countdescending.
Model solution
Checking your session…
What to watch for
- GROUP BY. Every selected column must either be in GROUP BY or sit inside an aggregate. SQLite accepts other columns and returns an arbitrary value for them; most databases raise an error.
- ORDER BY. Without ORDER BY the row order is not guaranteed, even if it looks stable. Rows that tie on the sort columns can come back in any order.
- Aggregate functions. Aggregates skip NULLs. AVG divides by the number of non-NULL values and COUNT(column) can be smaller than COUNT(*).
Related SQL challenges
- Salary Statistics per Department: Count, Avg, Min and MaxSimilar levelMedium
- Find the Best-Selling Products by QuantitySimilar levelMedium
- Count Orders by Status with GROUP BYEasierEasy
- Rank Products by Their Average Review RatingHarderHard
- Calculate Rating Variance per Product Without a VARIANCE FunctionHarderHard
Keep learning
- Lesson: GROUP BY
- Lesson: ORDER BY
- Lesson: Aggregate Functions
- All SQL practice challenges, by difficulty and topic
- SQL interview questions with answers
- SQL Playground: run any query on the same database