Virtual network service (VNet) endpoints will allow you to securely add Azure SQL DBs to your virtual network, fully removing public internet access to these resources. Service endpoints will provide direct connection from your virtual network to an Azure service, allowing you to use your virtual network's private address space to access supported Azure services. Traffic destined to Azure services through service endpoints will always remain on the Microsoft Azure backbone network. There won't be any additional cost to enabling service endpoints on your virtual networks.
Learn more about virtual network service endpoints.