Queries are processed by an optimizing query processor. It uses a subset of T-SQL for querying and due to lack of XML support, XQuery is not supported either. The current release does not support stored procedures or native XML data type either.
However, nested transactions are not supported, even though parallel transactions (on different tables) are. Like Microsoft SQL Server, SQL CE supports transactions, referential integrity constraints, locking as well as multiple connections to the database store. To meet the durability requirement the commit call on the transaction must specify the immediate flag.
Therefore, committed transaction changes can be lost. SQL CE databases can support ACID-compliance, but do not meet the durability requirement by default because AutoFlush buffers changes in memory (including enlisted ambient transactions and explicit SQL CE transactions that do not override the Commit() call with an CommitMode.Immediate value).
Windows Store apps for Windows 8 cannot use SQL Server Compact edition, or any other edition of SQL Server. SQL CE is optimized for an architecture where all applications share the same memory pool.
It has a disk footprint of less than 2 MB and a memory footprint of approximately 5 MB. Unlike other editions of Microsoft SQL Server, SQL CE runs in-process with the application which is hosting it. Future releases will unify the synchronization capabilities with Microsoft Synchronization Services. It also includes ADO.NET providers for data access using ADO.NET APIs, and built-in synchronization capabilities, as well as support for LINQ and Entity Framework. SQL Server Compact shares a common API with the other Microsoft SQL Server editions.