HardSQL challenge #223HAVINGSUBQUERYAGGREGATION

Users Above Avg Order Spend

Find users whose avg order value exceeds overall avg.

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 users whose avg order value exceeds overall avg.

A correct answer returns 55 rows with 2 columns: user_id, avg_user.

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
user_idavg_user
14064.75
54924.23
63701.8900000000003
73510.566666666666
82608.193333333333

First 5 of 55 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

  • Summarising many rows into one value with COUNT, SUM, AVG, MIN or MAX
  • Grouping rows with GROUP BY to get one result row per group
  • Filtering groups after aggregation with HAVING
  • Using the result of one query inside another

Hint and approach

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

Show the hint

AVG + HAVING

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. Group the rows by user_id, so the result has one row for each value.
  3. For each group, compute AVG(total).
  4. Filter the groups in HAVING: keep those where avg_user is greater than the value returned by a subquery.
  5. The subquery in HAVING runs once and returns a single value. It works like this:
    1. Read from the orders table.
    2. Aggregate over all the rows that are left: compute AVG(total). With no GROUP BY, the result is a single row.

Model solution

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What to watch for

  • HAVING. Conditions on single rows belong in WHERE and conditions on aggregates in HAVING. Putting a row filter in HAVING works, but it groups rows that are about to be thrown away.
  • GROUP BY. Every selected column must either be in GROUP BY or sit inside an aggregate. SQLite accepts other columns and returns an arbitrary value for them; most databases raise an error.
  • Subquery. A subquery compared with =, > or < must return exactly one row and one column. If it can return several rows, use IN or an aggregate.
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