Azure SQL Database

Azure SQL Database is a fully managed relational database service built on the Microsoft SQL Server engine. Unlike running SQL Server on a virtual machine, Azure SQL Database removes the overhead of patching, hardware management, and backup scheduling. Microsoft handles all infrastructure tasks while you focus entirely on your application and data.

Azure SQL Database offers two purchasing models. The DTU model bundles compute, memory, and I/O into a single unit called a Database Transaction Unit — simple but less flexible. The vCore model lets you choose CPU cores and memory independently, and supports Azure Hybrid Benefit for licence savings. For most new workloads, vCore is recommended.

Within the vCore model, three service tiers target different workloads. General Purpose suits most OLTP applications with balanced compute and storage. Business Critical provides ultra-low latency and built-in read replicas using in-memory technology. Hyperscale supports databases up to 100 TB with rapid horizontal scale-out.

An Azure SQL Database lives inside a logical SQL server — a management endpoint that hosts multiple databases and enforces firewall rules, Entra ID authentication, and auditing settings. You create the logical server first, then create one or more databases within it. Each database is billed and scaled independently.

By default, Azure SQL Database blocks all inbound connections. You must add server-level firewall rules to allow specific IP ranges, or enable the 'Allow Azure services' toggle to let other Azure resources connect. For production environments, use private endpoints inside a VNet to avoid exposing the database to the public internet entirely.

Azure SQL Database provides built-in high availability with no configuration required. In the General Purpose tier, data files are stored on Azure Premium Storage with automatic replication. In the Business Critical tier, an Always On availability group runs three to four replicas across availability zones for near-zero RPO. SLAs reach 99.99% uptime.

Azure SQL Database automatically takes full backups weekly, differential backups every 12 hours, and transaction log backups every 5-12 minutes. These backups enable Point-In-Time Restore (PITR), letting you recover your database to any second within the retention period — from 7 up to 35 days depending on your tier.

An elastic pool groups multiple Azure SQL Databases together so they share a fixed pool of DTUs or vCores. This is ideal for SaaS applications with many tenant databases that have unpredictable or offsetting workload peaks. Databases in a pool draw from the shared resource budget as needed, reducing per-database cost compared to provisioning resources individually.

Azure SQL Database encrypts all data at rest using Transparent Data Encryption (TDE) by default, and data in transit is always protected by TLS. Advanced Threat Protection detects anomalous database activity such as SQL injection attempts and flags them as security alerts. Enabling Auditing writes query logs to a storage account or Log Analytics workspace for compliance evidence.

Azure SQL Database supports dynamic scaling with minimal downtime. You can change the service tier or the number of vCores through the Azure portal, CLI, or API, and the change takes effect within seconds to minutes. This elasticity lets you scale up before a marketing event and scale back down afterwards, paying only for what you use when on the serverless tier.

The serverless compute tier within General Purpose automatically pauses the database after a configurable period of inactivity and resumes on the next connection. You are billed only for the seconds the database is active, making it highly cost-effective for development, testing, and intermittently used applications that don't need to be always-on.

Test your understanding of Microsoft Azure Fundamentals (AZ-900) concepts from this lesson.

In this lesson you learned: Azure SQL Database is a fully managed PaaS relational engine, the vCore model provides granular sizing and Hybrid Benefit support, and built-in high availability, automatic backups, and TDE are included at every tier. Next up we explore Azure Cosmos DB, Microsoft's globally distributed NoSQL service.