public override AlgebraNode VisitAggregateAlgebraNode(AggregateAlgebraNode node)
{
node.Input = VisitAlgebraNode(node.Input);
if (node.Input is NullScanAlgebraNode)
{
if (node.Groups != null && node.Groups.Length > 0)
{
// Grouped queries return nothing on empty input.
return(CreateNullScan(node.OutputList));
}
else
{
// Non-grouped aggregation. We return the result value of the aggregates
// executed against an empty input as a single row.
List <RowBufferEntry> outputList = new List <RowBufferEntry>();
List <ComputedValueDefinition> emptyValueList = new List <ComputedValueDefinition>();
foreach (AggregatedValueDefinition definedValue in node.DefinedValues)
{
IAggregator aggregator = definedValue.Aggregator;
aggregator.Init();
object emptyValue = aggregator.Terminate();
ComputedValueDefinition computedBufferedValue = new ComputedValueDefinition();
computedBufferedValue.Target = definedValue.Target;
computedBufferedValue.Expression = LiteralExpression.FromTypedValue(emptyValue, aggregator.ReturnType);
emptyValueList.Add(computedBufferedValue);
outputList.Add(computedBufferedValue.Target);
}
ConstantScanAlgebraNode constantScanAlgebraNode = new ConstantScanAlgebraNode();
constantScanAlgebraNode.DefinedValues = emptyValueList.ToArray();
constantScanAlgebraNode.OutputList = outputList.ToArray();
return(constantScanAlgebraNode);
}
}
return(node);
}
public void Init()
{
_sumAggregator.Init();
_count = 0;
}