aggregateRows method
An aggregate over the rows this query returns.
Follows countRows in every respect except which aggregate is written,
including the derived table a collapsing shape needs: SUM(Total) beside
an ORDER BY is not valid SQL, and beside a GROUP BY it is a different
question.
Implementation
MssqlQuery aggregateRows(MssqlExpression aggregate) =>
_aggregateOverResult(aggregate, 'aggregateRows()');