HardSQL challenge #247WINDOW FUNCTIONPARTITIONRANKING

Dense Rank Salaries Within Each Department

Return every employee with a dense rank of their salary inside their department.

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

Assign dense rank of salary within each department.

A correct answer returns 120 rows with 13 columns: id, first_name, last_name, email, department, department_id, title, salary, hire_date, manager_id, city, status, rnk.

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	rnk
100	Nancy	Thompson	nthompson43@corp.io	Customer Success	7	Senior CS Manager	203999	2023-01-23	10	New York	active	1
60	Maria	Garcia	mgarcia35@corp.io	Customer Success	7	CS Manager	191120	2016-11-09	9	Washington DC	active	2
15	Barbara	Baker	bbaker4@corp.io	Customer Success	7	Senior CS Manager	188280	2018-12-15	8	Philadelphia	on_leave	3
23	Melissa	Thomas	mthomas49@corp.io	Customer Success	7	VP Customer Success	178391	2024-09-09	7	San Francisco	active	4
103	Dorothy	Campbell	dcampbell66@corp.io	Customer Success	7	Senior CS Manager	165118	2017-01-14	5	Seattle	on_leave	5

First 5 of 120 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

Ranking rows with RANK() or DENSE_RANK() and handling ties
Restarting a window calculation for each group with PARTITION BY

Hint and approach

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

Show the hint

DENSE_RANK partition

Show the step-by-step approach

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

Read from the employees table.
Rank the rows with DENSE_RANK(), ordered by salary descending, restarting for each department. Tied rows share a rank and no rank number is skipped.

Model solution

Checking your session…

What to watch for

The rank restarts at 1 for each department and uses consecutive integers, so the highest rank in a department equals its number of distinct salary levels.

RANK() and DENSE_RANK(). RANK() skips numbers after a tie (1, 1, 3) and DENSE_RANK() does not (1, 1, 2). Filtering on rank <= N returns more than N rows when there are ties.
PARTITION BY. PARTITION BY is not GROUP BY: it keeps every row and only decides which rows a window function looks at.