HardSQL challenge #372WINDOW FUNCTIONPARTITIONCALCULATION

Salary Ratio to Department Avg

Find employees with highest ratio of salary to department average.

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 with highest ratio of salary to department average.

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, ratio.

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	ratio
55	Kenneth	Campbell	kcampbell32@corp.io	Legal	8	Legal Counsel	192220	2016-03-13	9	New York	active	1.7030815303102795
2	John	Miller	jmiller51@corp.io	Legal	8	Paralegal	191694	2021-08-09	NULL	San Diego	active	1.6984211365690287
11	Laura	Rivera	lrivera10@corp.io	Sales	3	Sales Manager	195759	2022-11-19	1	San Diego	active	1.6746866984699282
48	Steven	Nguyen	snguyen35@corp.io	Marketing	2	Content Lead	204449	2015-01-14	5	Phoenix	active	1.647309694001826
50	Paul	Robinson	probinson12@corp.io	Finance	5	Finance Manager	196032	2019-05-05	4	Jacksonville	active	1.613817289723473

First 5 of 120 rows. This is the output of the model solution on the practice database.

What you practise

Attaching a total or average to every row with an aggregate OVER ()
Restarting a window calculation for each group with PARTITION BY
Sorting the result with ORDER BY
Deriving a new column from an expression and naming it with an alias

Hint and approach

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

Show the hint

salary / AVG OVER 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.
Compute AVG(salary) as a window function over each department, so the group's value is repeated on every one of its rows.
Combine those values into ratio: salary * 1.0 / AVG(salary) OVER (PARTITION BY department).
Sort the result by ratio descending.

Model solution

Checking your session…

What to watch for

Window aggregates. A window aggregate keeps every row, while a plain aggregate collapses them. Mixing the two in one SELECT without GROUP BY is an error.
PARTITION BY. PARTITION BY is not GROUP BY: it keeps every row and only decides which rows a window function looks at.
Calculated columns. Dividing one integer by another truncates the result in SQLite. Multiply one side by 1.0 to get decimals.