HardSQL challenge #387WINDOW FUNCTIONROLLING WINDOWAGGREGATION

Max Density in 5-Day Window

Find highest average order value in rolling 5-day window.

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.

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The task

Find highest average order value in rolling 5-day window.

A correct answer returns 200 rows with 2 columns: order_date, avg_5d.

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
iduser_idtotaldiscountitem_countstatusorder_dateshipped_dateshipping_cityshipping_country
1432638.110.253cancelled2024-04-24NULLLos AngelesUSA
2829470.195delivered2024-03-152023-04-09ChicagoUSA
3136683.240.082delivered2023-02-152023-07-10Los AngelesUSA

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_dateavg_5d
2022-08-154181.625999999999
2022-07-244026.1619999999994
2023-03-263891.762
2022-06-283773.6159999999995
2024-10-113767.96

First 5 of 200 rows. This is the output of the model solution on the practice database.

What you practise

  • Limiting a window to nearby rows with ROWS BETWEEN
  • Sorting the result with ORDER BY

Hint and approach

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

Show the hint

AVG OVER rows

Show the step-by-step approach

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

  1. Read from the orders table.
  2. Compute AVG(total) as a window function over the current row and the 4 rows before it, ordered by order_date.
  3. Sort the result by avg_5d descending.

Model solution

Checking your session…

What to watch for

  • Window frames. A ROWS frame counts rows, not time. "6 PRECEDING" is six rows back, which is six days only when there is exactly one row per day.
  • ORDER BY. Without ORDER BY the row order is not guaranteed, even if it looks stable. Rows that tie on the sort columns can come back in any order.
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