how to execute my own sql by OFBiz delegator

[sheng]

Hello everyone,
I have an entity defined as:
<entity entity-name="Commodity">
      <field name="quantity" type="long"/>
      <field name="price" type="long"/>
</entity>

How can l get the following sql execution result by OFBiz delegator?
SELECT (quantity*price)/SUM(quantity) average FROM commodity WHERE price>100;

Thanks a lot