Available in preview today, you can use Azure SQL Database Query Store. This feature enables you to easily identify queries that used to perform well but now perform poorly. It accumulates a history of each query, including its associated plans, run-time statistics, and information about resource consumption.
Query Store separates collected data by time windows, allowing you to see changes in database utilization and performance over time. If a query generates a different plan, you can use Query Store to analyze the query plan changes, possible performance degradation, or even to force the system to use a particular plan for your query.
Query Store is a database level feature. SQL Server Management Studio or another Transact-SQL delivery tool is required to implement and manage Query Store.
For more information, visit the Query Store
page on MSDN.