HardSQL challenge #294GROUP BYDATEANALYTICS

Find Churned Customers with No Orders in the Last 90 Days

Return the users whose most recent order is more than 90 days old.

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 users who have not ordered in last 90 days.

A correct answer returns 114 rows with one column: user_id.

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

The result has the columns listed above and 114 rows. This query depends on today's date, so its values change from day to day and no fixed rows are shown here.

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
  • Working with dates in SQLite: strftime, julianday and DATE

Hint and approach

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

Show the hint

MAX(order_date)

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 MAX(order_date).
  4. Filter the groups in HAVING: keep those where MAX(order_date) is less than the date 90 days before today.

Model solution

Checking your session…

What to watch for

The cutoff is measured from today with DATE('now', '-90 day'). This dataset ends in December 2024, so every customer who ever ordered now counts as churned. Users who never ordered are absent, because the query reads only the orders table.

  • 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.
  • Date functions. These date functions are SQLite syntax. MySQL uses DATE_FORMAT and DATEDIFF, PostgreSQL uses TO_CHAR, EXTRACT and date subtraction.
Solve This SQL Challenge

Keep learning