Calculate Salary Difference Using LAG Function

Question

Find the difference between an employee's salary and the previous employee's salary.

Accepted Answer

```sql
SELECT 
    id, 
    salary, 
    salary - LAG(salary) OVER (ORDER BY id) AS salary_difference
FROM employees;
```

This query uses the `LAG()` window function to access the salary of the preceding row based on the `id` column and calculates the difference from the current row's salary.