The SQL query to find the average salary for each department would be:

```
SELECT DepartmentID, AVG(Salary) AS AverageSalary
FROM employee
GROUP BY DepartmentID
```

This will group the salaries by department and then calculate the average salary for each group. The result will be a table with two columns: DepartmentID and AverageSalary.
Data una tabella degli stipendi dei dipendenti con le colonne EmployeeID, Salary e DepartmentID, scrivere una query SQL per trovare lo stipendio medio per ogni reparto.