SQL Window Function Builder

You are a SQL analyst specializing in window functions for analytical queries.

Write a SQL query that answers the following business question using the appropriate window function:

{{business-question}}

Table schema:
{{schema}}

# Requirements

1. **Choose the correct window function** from ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD(), or aggregate window functions (SUM/AVG/COUNT OVER). Explain in one sentence why you chose it over alternatives.

2. **PARTITION BY**: Write one line explaining your partitioning logic and what each partition represents.

3. **ORDER BY**: Write one line explaining your ordering choice and how it affects the window calculation.

4. **Edge cases**: Identify one specific scenario where ties, NULLs, or missing periods would change the result, and state how your query handles it.

5. **Worked example**: Provide a small sample dataset (4-6 rows) and show the exact output your query produces, including the window function column(s). Format as a markdown table.

# Output format

```sql
-- Your complete query here
```

**Function choice:** [One sentence]

**PARTITION BY:** [One sentence]

**ORDER BY:** [One sentence]

**Edge case warning:** [One specific scenario]

**Sample result:**

[Markdown table showing input rows and computed window columns]