public IRowCursor Select(SelectableRange range)
{
// If it's an empty range,
if (range.IsEmpty)
return new SimpleRowCursor(0);
List<IRowCursor> cursors = new List<IRowCursor>();
// For each range pair,
ISelectableRangeEnumerator en = range.GetEnumerator();
while (en.MoveNext()) {
// The range pair information,
SqlObject[] lower = en.LowerBound;
SqlObject[] upper = en.UpperBound;
bool lowerAtFirst = en.IsLowerBoundAtFirst;
bool upperAtLast = en.IsUpperBoundAtLast;
IRowCursor cursor = RangeCursor(lower, upper, lowerAtFirst, upperAtLast);
// If the pair resolves to something, add it to the iterator set.
if (cursor != null && cursor.Count > 0)
cursors.Add(cursor);
}
return new SelectedRowCursor(new GroupedRowCursor(cursors));
}
private SubsetTable FilterByIndex(ITable table, IIndexSetDataSource index, Expression order, SelectableRange range)
{
// Select from the index and return the subset
IRowCursor rows = index.Select(range);
SubsetTable filteredTable = new SubsetTable(table, rows);
filteredTable.OrderComposite = order;
// If the number of rows selected from the index is the same as the
// original table, then it is safe for index requests to fallthrough to the
// parent.
long selectCount = rows.Count;
long originalCount = table.RowCount;
if (selectCount == originalCount)
filteredTable.IndexRequestFallthrough = true;
// Assert we didn't select more than in the original context
if (selectCount > originalCount)
throw new ApplicationException( "Index found more values than in parent table.");
return filteredTable;
}
public double ProbabilityEstimate(SelectableRange rangeSet)
{
// If we don't have any information, return the worst case of 1.0. This
// will happen if the data set is very small.
if (totalSize == 0) {
return 1.0d;
}
// How many samples intersect the range set?
IRangeIntersector comparator = rangeSet.Intersector;
int intersect_count = 0;
for (int i = 0; i < divisionPoints.Length; ++i) {
if (comparator.ValueIntersects(new SqlObject[] { divisionPoints[i] })) {
++intersect_count;
}
}
// The worst case is ((1 + intersect_count) * row_to_samples) for single
// value range sets. This is the general heuristic we will use even
// though the worst case could be higher for multi valued ranges.
double iCount = intersect_count + 1;
// Probability
double probability = iCount / DivisionPointCount;
return System.Math.Min(probability, 1.0d);
}
