I'm not sure if this is ij or derby proper, but the concat operator || should work for just about any data type. Derby is zero maintenance, but data rarely is, and a good sql interface is important. Often it's very convenient to write a query that generates other sql statements and that's difficult w/o concatination.
e.g. create a table with a timestamp column, assume that the column name is originated.
Try the following query:
ij> select month(originated) || '-' || year(originated) from review;
get the following error:
ERROR 42846: Cannot convert types 'INTEGER' to 'VARCHAR'.
The conversion to a string should pretty much work all the time unless the operand is some sort of blob type.