1. A method for processing a program statement in a database query language, the program statement corresponding to a plurality of operators, wherein an operator tree can be identified based upon the plurality of operators, the operator tree comprising a parent operator node, the parent operator node possibly associated with one or more child operator nodes, the method comprising: (a) identifying whether one or more child nodes exist; (b) for each of the identified one or more child nodes, determining if the child node relates to an operator for which top-down processing can be performed; (c) calling and executing the operators from (a) for the child nodes that are eligible for top-down processing; (d) generating output results for a child node that is not eligible for top-down processing; and (e) outputting the output results to a data stream.