HardSQL challenge #237WINDOW FUNCTIONNTILERANKING

Find the Top 10% Most Expensive Products with NTILE

Return the products that fall in the highest tenth by price.

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

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The task

Find products in top 10% by price.

A correct answer returns 12 rows with 11 columns: id, name, category, price, cost, stock, sku, status, rating, review_count, bucket.

Tables used in this challenge

`products` 120 rows

id INTEGER (PK) · name TEXT · category TEXT · price REAL · cost REAL · stock INTEGER · sku TEXT · status TEXT · rating REAL · review_count INTEGER

First 3 rows of the products table
id	name	category	price	cost	stock	sku	status	rating	review_count
1	Play Kitchen Deluxe	Toys	1786.38	589.51	257	SKU-000001	active	4	57
2	Micro-Cut Paper Shredder 8-Sheet	Office Supplies	907.93	281.46	131	SKU-000002	active	2.5	447
3	4K Dual Dash Camera	Automotive	568.89	204.8	176	SKU-000003	active	4.1	29

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	name	category	price	cost	stock	sku	status	rating	review_count	bucket
68	Single Origin Coffee 500g	Food & Beverage	1991.75	657.28	195	SKU-000068	active	4.7	131	1
108	Succulent Plant Set	Home & Garden	1990.16	616.95	107	SKU-000108	discontinued	4	224	1
110	The Manager's Path	Books	1979.28	989.64	48	SKU-000110	active	4.9	381	1
61	2000A Jump Starter Pack	Automotive	1948.86	915.96	338	SKU-000061	active	4.3	43	1
28	Japanese Green Tea 50 bags	Food & Beverage	1937.51	620	488	SKU-000028	active	2.7	5	1

First 5 of 12 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

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 products table.
2. Deal the rows into 10 equal-sized buckets with NTILE(10), ordered by price 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(10) deals the sorted rows into ten buckets of as equal a size as possible, and bucket 1 is the top tenth. The buckets are sized by row count, so two products at the same price can land in different buckets.

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.

Solve This SQL Challenge

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Same technique, other tables

More practice on this pattern with different columns:

Keep learning

Lesson: Window Functions
Lesson: SQL Subqueries
Lesson: WHERE Clause
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