Which of the following service tiers is NOT available for Azure SQL Database?

The service tier that is not available for Azure SQL Database is the Enterprise tier. Azure SQL Database offers various service tiers to accommodate different performance and resource requirements. The Basic, Standard, and Premium tiers are designed to cater to small to medium workloads and offer specific levels of compute, storage, and throughput.

The Basic tier is intended for development and testing workloads or small applications, the Standard tier suits most applications with moderate transaction workloads, and the Premium tier offers high-performance features and scalability for mission-critical applications. However, there is no designated Enterprise tier within Azure SQL Database's offerings. Microsoft has structured its service tiers to provide flexibility and options tailored to the needs of various sizes and types of applications, but the Enterprise designation specifically does not apply here.