RQL now includes a basic library of string functions. You can use these to slice and group your data in arbitrary ways. For example, "email domains with the most events in the past hour":
SELECT substring(person.email, locate('@', person.email)), count(*) FROM item_occurrence WHERE timestamp >= unix_timestamp() - 3600 AND person.email IS NOT NULL GROUP BY 1 ORDER BY 2 DESC
The new functions: concat, concat_ws, lower, upper, left, right, substring, locate, length, char_length. The functions are implemented to be compatible with MySQL; see the RQL docs for details.