HardSQL challenge #255WINDOW FUNCTIONNTILERANKING

Top Revenue Orders

Find orders contributing to top 20% revenue.

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

Solve This SQL Challenge

The task

Find orders contributing to top 20% revenue.

A correct answer returns 40 rows with 11 columns: id, user_id, total, discount, item_count, status, order_date, shipped_date, shipping_city, shipping_country, bucket.

Tables used in this challenge

`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
id	user_id	total	discount	item_count	status	order_date	shipped_date	shipping_city	shipping_country
1	43	2638.11	0.25	3	cancelled	2024-04-24	NULL	Los Angeles	USA
2	8	2947	0.19	5	delivered	2024-03-15	2023-04-09	Chicago	USA
3	136	683.24	0.08	2	delivered	2023-02-15	2023-07-10	Los Angeles	USA

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
id	user_id	total	discount	item_count	status	order_date	shipped_date	shipping_city	shipping_country	bucket
123	53	4997.15	0.21	4	processing	2023-05-21	NULL	Chicago	USA	1
114	118	4980.63	0.05	6	delivered	2023-03-18	2024-12-10	Los Angeles	USA	1
192	49	4936.98	0.06	1	refunded	2023-01-12	NULL	Charlotte	USA	1
94	7	4926.49	0.05	4	processing	2023-08-24	NULL	Austin	USA	1
127	5	4924.23	0.22	1	delivered	2024-05-18	2024-03-21	Phoenix	USA	1

First 5 of 40 rows. This is the output of the model solution on the practice database. The task does not fix a sort order, so your rows may come back in a different order.

What you practise

Filtering rows with a WHERE condition
Querying the result of another query with a subquery in FROM
Splitting rows into equal-sized buckets with NTILE()

Hint and approach

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

Show the hint

NTILE(5)

Show the step-by-step approach

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

Build an inner query first (a derived table):
1. Read from the orders table.
2. Deal the rows into 5 equal-sized buckets with NTILE(5), ordered by total descending.
Filter in WHERE: keep the rows where bucket equals 1. The filter sits in the outer query because a window function cannot be tested in the WHERE clause of the query that computes it.

Model solution

Checking your session…

What to watch for

NTILE(). NTILE() balances the number of rows per bucket, not the values. Rows with the same value can end up in different buckets.
Derived table. Columns computed in the inner query are only visible outside under their alias, so every calculated column there needs a name.
WHERE. WHERE is evaluated before the SELECT list, so it cannot use a column alias defined there or the result of an aggregate.