HardSQL challenge #356WINDOW FUNCTIONRUNNING AVERAGEANALYTICS

Cumulative Density Orders

Find cumulative average order value over time.

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 cumulative average order value over time.

A correct answer returns 200 rows with 2 columns: order_date, cum_avg.

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
order_date	cum_avg
2022-01-06	1843.49
2022-01-10	2881.965
2022-01-15	2305.3533333333335
2022-01-16	2576.93
2022-01-17	2894.298

First 5 of 200 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

Accumulating a value row by row with an ordered window

Hint and approach

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

Show the hint

AVG OVER

Show the step-by-step approach

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

Read from the orders table.
Compute AVG(total) as a running window function: it covers the rows from the start up to the current one, ordered by order_date.

Model solution

Checking your session…

What to watch for

Running totals. With ORDER BY and no frame, rows that tie on the sort column are added together in one step. Use ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW for a strict row-by-row total.