HardSQL challenge #207WINDOW FUNCTIONPERCENTAGEAGGREGATION

Calculate Each Order's Percentage of Total Revenue

Return every order with the percentage it contributes to total revenue.

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 each order’s contribution percentage to total revenue.

A correct answer returns 200 rows with 3 columns: id, total, pct.

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
idtotalpct
12638.110.5162937813010847
229470.5767453872258157
3683.240.1337141222830561
43920.440.767253371528869
51120.990.2193843948511256

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

  • Attaching a total or average to every row with an aggregate OVER ()
  • 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

SUM() OVER

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 SUM(total) with an empty OVER (), so the figure for the whole result is repeated on every row.
  3. Combine those values into pct: (total * 100.0) / SUM(total) OVER ().

Model solution

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What to watch for

An empty OVER () makes the window the whole result, so SUM(total) OVER () repeats the grand total on every row without collapsing them. The percentages add up to 100.

  • 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.
  • Calculated columns. Dividing one integer by another truncates the result in SQLite. Multiply one side by 1.0 to get decimals.
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