8. The method of claim 1 wherein: each of the query plans is associated with a respective query plan tree comprising one or more nodes; and evaluating each of the query plans comprises adding a node cost associated with a type of each of the nodes in the respective query plan tree to a query plan cost for that query plan.
8. The method of claim 1 wherein: each of the query plans is associated with a respective query plan tree comprising one or more nodes; and evaluating each of the query plans comprises adding a node cost associated with a type of each of the nodes in the respective query plan tree to a query plan cost for that query plan. 9. The method of claim 8 wherein when one of the nodes is a join node, the node cost for the join node is based on an aggregation of a cost of each sub-query plan associated with children of the join node.