How can I perform this kind of range join query using DPL?

Question

How can I perform this kind of range join query using DPL?
SELECT * from t where 1<=t.a<=2 and 3<=t.b<=5
In this pdf : http://www.oracle.com/technology/products/berkeley-db/pdf/performing%20queries%20in%20oracle%20berkeley%20db%20java%20edition.pdf,
It shows how to perform "Two equality-conditions query on a single primary database" just like SELECT * FROM tab WHERE col1 = A AND col2 = B using entity join class, but it does not give a solution about the range join query.

Answer 1

I'm sorry, I think I've misled you. I suggested that you perform two queries and then take the intersection of the results. You could do this, but the solution to your query is much simpler. I'll correct my previous message.
Your query is very simple to implement. You should perform the first part of query to get a cursor on the index for 'a' for the "1<=t.a<=2" part. Then simply iterate over that cursor, and process the entities where the "3<=t.b<=5" expression is true. You don't need a second index (on 'b') or another cursor.
This is called "filtering" because you're iterating through entities that you obtain from one index, and selecting some entities for processing and discarding others. The white paper you mentioned has an example of filtering in combination with the use of an index.
An alternative is to reverse the procedure above: use the index for 'b' to get a cursor for the "3<=t.b<=5" part of the query, then iterate and filter the results based on the "1<=t.a<=2" expression.
If you're concerned about efficiency, you can choose the index (i.e., choose which of these two alternatives to implement) based on which part of the query you believe will return the smallest number of results. The less entities read, the faster the query.
Contrary to what I said earlier, taking the intersection of two queries that are ANDed doesn't make sense -- filtering is the better solution. However, taking the union of two queries does make sense, when the queries are ORed. Sorry for the confusion.
--mark