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Detect stale invoices

Goal -- WPM

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Exercise Algorithm Area
1SELECT i.id, i.customer_id, i.due_date

2FROM invoices i

3LEFT JOIN payments p ON p.invoice_id = i.id

4WHERE p.id IS NULL AND i.due_date < date('now', '-30 day');
Algorithm description viewbox

Detect stale invoices

Algorithm description:

Identify outstanding invoices that have surpassed the 30-day window without any payment events.

Algorithm explanation:

Use a LEFT JOIN to find invoices lacking payment rows and filter by due_date older than 30 days relative to today, ensuring insurance for missing data.

Pseudocode:

SELECT invoice.id, invoice.customer_id, invoice.due_date
FROM invoices
LEFT JOIN payments ON payments.invoice_id = invoice.id
WHERE payments.id IS NULL
  AND invoice.due_date < TODAY() - 30