If you have a web-application that uses a SQL Server database then you might have to buy an external connector license (this I did not know before today – luckily we have a licensing guy in our org.)
External Connector Licensing:
An external user is a person who is not an employee or similar personnel of the company or its affiliates, and is not someone to whom you provide hosted services. An EC license assigned to a server permits access by any number of external users, as long as that access is for the benefit of the licensee and not the external user.
Anyways, the only time you wont need an external connector license for your SQL Server database is when your installation is licensed by the processor.
Per Processor Licensing
Under the Per Processor model, you acquire a Processor License for each processor in the server on which the software is running. A Processor License includes access for an unlimited number of users to connect from either inside the local area network (LAN) or wide area network (WAN), or outside the firewall (via the Internet). You do not need to purchase additional server licenses, CALs, or Internet Connector Licenses.