Write SQL query to solve given problem: Among all orders shipped, calculate the percentage of orders shipped at least 3 days before the required date.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT COUNT(CASE WHEN JULIANDAY(t1.shippeddate) - JULIANDAY(t1.requireddate) > 3 THEN T1.customerNumber ELSE NULL END) FROM orders AS T1 INNER JOIN orderdetails AS T2 ON T1.orderNumber = T2.orderNumber WHERE T1.status = 'Shipped'