The following is a non-exhaustive list of SQL features that JoSQL does NOT currently support (please note no guarantee is made as to whether or when any of them will be supported either):

• Joins - in general, when converting data from a RDBMS to objects, joins are used to "gather" the information from relevant tables to form the "record" that holds the object data. However since JoSQL already works on objects, joining objects together is a fairly pointless exercise. Also, the amount of work to handle the joins is not worth the small gain that it would bring.
• UNION [ALL], MINUS - these are operations that are potentially beneficial for the developer in JoSQL. However since it is relatively easy to perform both operations in Java code via the Collections framework and use JoSQL to find the relevant sets of objects these features aren't considered a high priority.

There are probably lots of other (and mostly proprietary) SQL features that JoSQL does not support. Please note that the design aim of JoSQL is NOT to provide comprehensive SQL functionality, rather it is to allow Java Developers to perform painful tasks relating to collections of objects easily and quickly. If there a feature that you feel should be added to JoSQL please feel free to  request that it is added.