1. A method for generating machine executable code for implementing a query of a database, the database having tables and records of data, comprising the steps of: receiving a subject query; forming an execution plan corresponding to the subject query, the execution plan having a sequence of pieces and corresponding processes for implementing the pieces; and for each piece of the plan, (a) generating source code using different code generation techniques as a function of any combination of data characteristics, current conditions and workload, and (b) compiling the generated source code to form machine executable code for implementing the subject query, said compiling being in a manner that optimizes total query processing time, including, compilation time and execution time.