Returns a set of values of expression calculated over dimensions. The result can be compared to the expression column of a 'local chart', evaluated in the context where the aggr function resides. Each dimension must be a single field. It cannot be an expression (calculated dimension).
If the expression argument is preceded by the nodistinct qualifier, each combination of dimension values may generate more than one return value, depending on underlying data structure. If the expression argument is preceded by the distinct qualifier or if no qualifier is used at all, each combination of dimension values will generate only one return value.
By default, the aggregation function will aggregate over the set of possible records defined by the selection. An alternative set of records can be defined by a set expression.
