What is SQL Azure?
SQL Azure is a cloud based relational database as a Service offered by Microsoft. Conceptually it is SQL server in the cloud.
What is cloud computing?
Cloud computing is a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.
SQL Azure Pricing Overview:-
Compute time, measured in service hours: Windows Azure compute hours are charged only when your application is deployed. When developing and testing your application, developers will want to remove the compute instances that are not being used to minimize compute hour billing.
The standard pay-as-you-go pricing for Windows Azure compute is as follows:
Extra small instance**: $0.05 per hour
Small instance (default): $0.12 per hour
Medium instance: $0.24 per hour
Large instance: $0.48 per hour
Extra Large instance: $0.96 per hour
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I have not included the questions specific to unsupported features because it keeps on changing. Read general guidelines and limitations. Also note that SQL Azure is evolving very fast and it is important to keep a tab on the features that are added in service releases.