HardSQL challenge #242WINDOW FUNCTIONNTILERANKING

Top 10% Salaries

Find employees in top 10% salary bracket.

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

Solve This SQL Challenge

The task

Find employees in top 10% salary bracket.

A correct answer returns 12 rows with 13 columns: id, first_name, last_name, email, department, department_id, title, salary, hire_date, manager_id, city, status, bucket.

Tables used in this challenge

`employees` 120 rows

id INTEGER (PK) · first_name TEXT · last_name TEXT · email TEXT · department TEXT · department_id INTEGER · title TEXT · salary REAL · hire_date TEXT · manager_id INTEGER · city TEXT · status TEXT

First 3 rows of the employees table
id	first_name	last_name	email	department	department_id	title	salary	hire_date	manager_id	city	status
1	William	Lewis	wlewis18@corp.io	Customer Success	7	Senior CS Manager	61774	2022-07-24	NULL	San Diego	active
2	John	Miller	jmiller51@corp.io	Legal	8	Paralegal	191694	2021-08-09	NULL	San Diego	active
3	Daniel	Rivera	drivera50@corp.io	Engineering	1	VP Engineering	135067	2016-06-06	NULL	Houston	active

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	first_name	last_name	email	department	department_id	title	salary	hire_date	manager_id	city	status	bucket
48	Steven	Nguyen	snguyen35@corp.io	Marketing	2	Content Lead	204449	2015-01-14	5	Phoenix	active	1
100	Nancy	Thompson	nthompson43@corp.io	Customer Success	7	Senior CS Manager	203999	2023-01-23	10	New York	active	1
111	John	Lee	jlee7@corp.io	Operations	6	Operations Analyst	203467	2015-03-19	9	Seattle	active	1
106	Donna	Johnson	djohnson40@corp.io	Engineering	1	VP Engineering	199029	2018-06-21	2	Jacksonville	active	1
26	Matthew	Wilson	mwilson27@corp.io	Marketing	2	CMO	196530	2015-10-03	3	Columbus	active	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 employees table.
2. Deal the rows into 10 equal-sized buckets with NTILE(10), ordered by salary 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.