Grouping and aggregation

Apart from the joins, the groupping with subsequent aggregation represents the central type of transformations on data stocks which have to be described with the help of query expressions and accordingly supported. The formulation of grouping and aggregation in XQuery is oriented towards a mixture of SQL and OQL. A further distinction should be made whether the grouping which always represents an aggregation of the data stock is done along a XML hierarchy or with regard to equal values usually within a "flat" XML document. The relationships and differences are discussed on the following pages.

• Grouping according to structure
• Grouping according to equality of values
• Aggregation functions
• Grouping via several attributes
• Group filtering and sorting
• Multiple grouping
• Nested grouping

Source: "XQuery – Grundlagen und fortgeschrittene Methoden", dpunkt-Verlag, Heidelberg (2004)