Azure SQL Database is a managed relational database service offered by Microsoft Azure. It provides scalable and fully managed SQL Server databases in the cloud. The pricing for Azure SQL Database is based on various factors, including the service tier, performance level, and other optional features. Here are the key factors that affect the pricing of Azure SQL Database:

1. Service Tier: Azure SQL Database offers several service tiers, each designed for different workloads and performance levels. The available service tiers include Basic, Standard, Premium, General Purpose, Business Critical, and Hyperscale. The pricing varies significantly between these tiers, with higher tiers offering better performance and features.

2. Performance Level: Within each service tier, you can choose different performance levels, typically measured in terms of Database Transaction Units (DTUs) or vCores. DTUs are a simplified measure of database performance that combines CPU, memory, and I/O resources. vCores provide more granular control over resources. Higher performance levels come with higher pricing.

3. Database Size: The amount of storage required for your database also affects the pricing. Azure SQL Database offers a range of storage options, and you pay based on the provisioned storage capacity. You can choose the amount of storage needed to accommodate your data.

4. Database Redundancy: Azure SQL Database allows you to choose the level of redundancy for your database. Options include no redundancy (locally redundant), zone redundancy, and geo-redundancy. Higher redundancy levels come with additional costs but provide greater availability and data durability.

5. Optional Features: Azure SQL Database offers various optional features and add-ons, such as advanced threat protection, automatic tuning, backup retention, and active geo-replication. These features may have additional costs associated with them.

6. License Type: Azure SQL Database offers two licensing models: License Included and Bring Your Own License (BYOL). With License Included, the cost of SQL Server software is included in the service pricing. With BYOL, you are responsible for providing your SQL Server licenses, which can affect the overall pricing.

7. Reserved Capacity: Azure offers reserved capacity options that allow you to commit to a specific amount of resources for a one- or three-year term. This can provide cost savings compared to pay-as-you-go pricing.