Azure table storage vs Windows Azure SQL database

What is Windows Azure SQL database?

Think of Windows Azure SQL as the cloud evolution of your on premises relational database that supports standard relational principles and practices such as ACID transactions and server side execution through stored procedures.

When should I use SQL Azure? 

As a general rule use SQL Azure when you need structure, your database mightn't be over 500GB and you need to provide visualisation and BI reporting using out of the box reporting tools.

What is Azure table storage?

Azure table storage is Microsoft's cloud offering of a NoSQL database.

When should I use Azure table storage?

As a general rule use Azure table storage when you need to store significantly large data volumes, you need a flexible data schema and you need your data geo-replicated for additional durability in case of disaster.

Decision trees - Azure table storage Azure SQL or On Prem

Figure 1 - Choosing Between SQL Database and On-Premise SQL Server (source Technet)










Figure 2 - SQL Database Choices  (source Technet)



Figure 3 - Evaluating Compliance Factors Related to SQL Database vs. On-Premise Data Hosting (source Technet)

SQL Azure editions

*Note: The flow charts above are based on the Web and Business editions which will be  retired in September 2015 and replaced with Basic, Standard and Premium editions.

Service Tier/Performance Level	DTU	MAX DB Size	Max Concurrent Requests	Max Sessions	Benchmark Transaction Rate	Predictability
Basic	5	2 GB	30	300	16,600 transactions per hour	Good
Standard/S0	10	250 GB	60	600	521 transactions per minute	Better
Standard/S1	20	250 GB	90	900	934 transactions per minute	Better
Standard/S2	50	250 GB	120	1,200	2,570 transactions per minute	Better
Standard/S3*	100	250 GB	200	2,400	5,100 transactions per minute	Better
Premium/P1	100	500 GB	200	2,400	105 transactions per second	Best
Premium/P2	200	500 GB	400	4,800	228 transactions per second	Best
Premium/P3	800	500 GB	1,600	19,200	735 transactions per second	Best

References

https://msdn.microsoft.com/en-us/library/azure/jj553018.aspx

http://social.technet.microsoft.com/wiki/contents/articles/3398.windows-azure-sql-database-delivery-guide-for-business-continuity.aspx

https://msdn.microsoft.com/en-us/library/azure/ee336279.aspx

https://msdn.microsoft.com/en-us/library/azure/dn741330.aspx