Most SQL-based XML vendor support is through interoperation and not integration. One reason for this is that XML is inherently hierarchical and SQL is supposedly not. This paper demonstrates how ANSI SQL along with its relational Cartesian product model can naturally perform complete and flexible hierarchical query processing. With this ANSI SQL inherent hierarchical processing capability, native XML data can be fully and seamlessly integrated into SQL processing and operated on at a full hierarchical level. This paper will describe the basic stages involved in this hierarchical SQL processing: hierarchical data modeling, hierarchical working set creation, and hierarchical Cartesian product processing. These processes enable a complete relational, XML, and legacy data integration which maintains ANSI SQL compatibility even while performing the most complex multi-leg hierarchical processing, and includes the dynamic, direct, and controlled hierarchical joining of hierarchical structures. Also covered are ANSI SQL hierarchical support features: hierarchical SQL views, hierarchical data filtering, and hierarchical optimization. These make standard SQL a well rounded and complete hierarchical processor. With this full hierarchical level of processing established, it will be shown how the relational Cartesian product engine can be seamlessly replaced with a hierarchical engine, greatly increasing processing and memory utilization, and enabling advanced XML hierarchical data capabilities.