HardSQL challenge #222JOINGROUP BYORDER BY

Find the City with the Highest Total Revenue

Return the customer city that generated the most order revenue.

The challenge runs on the SQLabHub practice database (SQLite) and uses the users and orders tables. You can solve it in the browser, with nothing to install.

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The task

Find city with highest total revenue.

A correct answer returns 1 row with 2 columns: city, revenue.

Tables used in this challenge

users 150 rows

id INTEGER (PK) · first_name TEXT · last_name TEXT · email TEXT · phone TEXT · city TEXT · country TEXT · created_at TEXT · status TEXT · is_premium INTEGER

First 3 rows of the users table
idfirst_namelast_nameemailphonecitycountrycreated_atstatusis_premium
1JenniferTorresjennifer.torres57@icloud.com+1-263-376-2371HoustonCanada2024-04-13active0
2DonnaAdamsdonna.adams52@gmail.com+1-753-780-6670Fort WorthCanada2020-09-15inactive0
3KennethYoungkenneth.young94@proton.me+1-440-743-9503AustinUSA2023-09-05active0

orders 200 rows

id INTEGER (PK) · user_id INTEGER · total REAL · discount REAL · item_count INTEGER · status TEXT · order_date TEXT · shipped_date TEXT · shipping_city TEXT · shipping_country TEXT

First 3 rows of the orders table
iduser_idtotaldiscountitem_countstatusorder_dateshipped_dateshipping_cityshipping_country
1432638.110.253cancelled2024-04-24NULLLos AngelesUSA
2829470.195delivered2024-03-152023-04-09ChicagoUSA
3136683.240.082delivered2023-02-152023-07-10Los AngelesUSA

The first rows of each table are shown. See how all the tables relate on the database schema page.

Expected output

Expected output of the challenge
cityrevenue
Indianapolis62099.26

The complete result: 1 row. 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
  • Combining rows from two tables on a matching key with an inner join
  • Sorting the result with ORDER BY
  • Returning only the first rows with LIMIT

Hint and approach

Try the challenge first. Open these only when you need them.

Show the hint

JOIN users + orders

Show the step-by-step approach

How the model solution is built, in the order the database evaluates it:

  1. Read from the users table.
  2. Join orders on users.id = orders.user_id.
  3. Group the rows by users.city, so the result has one row for each value.
  4. For each group, compute SUM(orders.total).
  5. Sort the result by revenue descending.
  6. Keep only the first row with LIMIT 1.

Model solution

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What to watch for

The city comes from the users table, so this is where customers live, not where orders were shipped. Sorting the grouped totals and taking one row drops any city tied for first.

  • INNER JOIN. An inner join drops rows that have no partner on the other side, and it repeats a row once for every match, which inflates SUM and COUNT.
  • 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.
  • LIMIT. LIMIT without ORDER BY returns an arbitrary set of rows. LIMIT is also dialect-specific: SQL Server uses TOP and Oracle uses FETCH FIRST.
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Same technique, other tables

More practice on this pattern with different columns:

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