You're building a database for testing purposes that will be used less than 8 hours a day. It's expected to be 20 GB in size. What is your most cost-effective option?

Choosing the serverless option for a database expected to be used less than 8 hours a day and sized at 20 GB is the most cost-effective solution because serverless databases in Azure automatically scale based on demand. This means that you only pay for the storage consumed and the compute resources when the database is actively being used.

In a scenario where a database is not constantly in use, such as when it is only accessed for part of the day, serverless can save money since the compute resources can automatically auto-pause during idle times and auto-resume when activity starts again. This dynamic scaling provides significant cost savings for workloads with variable usage patterns compared to options that require continuous capacity provisioning.

In contrast, options like the Standard Tier Database or Elastic Pool might incur higher costs due to their continuous compute allocation, regardless of the actual usage over the course of the day. The Basic Tier could be less expensive but may not provide the necessary flexibility or scalability required for sporadic workloads, making serverless a better fit for your specific needs in this case.