public FunctionTable AsGroup()
{
// TODO: create a new table ...
wholeTableAsGroup = true;
wholeTableGroupSize = ReferenceTable.RowCount;
// Set up 'whole_table_group' to the list of all rows in the reference
// table.
var en = ReferenceTable.GetEnumerator();
wholeTableIsSimpleEnum = en is SimpleRowEnumerator;
if (!wholeTableIsSimpleEnum)
{
wholeTableGroup = new List <int>(ReferenceTable.RowCount);
while (en.MoveNext())
{
wholeTableGroup.Add(en.Current.RowId.RowNumber);
}
}
// Set up a group resolver for this method.
groupResolver = new TableGroupResolver(this);
return(this);
}
public override void Release()
{
// We unlock the reference table.
// NOTE: This cause the reference table to unlock twice when we use the
// 'MergeWith' method. While this isn't perfect behaviour, it
// means if 'MergeWithReference' isn't used, we still maintain a safe
// level of locking.
ReferenceTable.Release();
}
public ITable MergeWith(ObjectName maxColumn)
{
var table = ReferenceTable;
IList <int> rowList;
if (wholeTableAsGroup)
{
// Whole table is group, so take top entry of table.
rowList = new List <int>(1);
var rowEnum = table.GetEnumerator();
if (rowEnum.MoveNext())
{
rowList.Add(rowEnum.Current.RowId.RowNumber);
}
else
{
// MAJOR HACK: If the referencing table has no elements then we choose
// an arbitrary index from the reference table to merge so we have
// at least one element in the table.
// This is to fix the 'SELECT COUNT(*) FROM empty_table' bug.
rowList.Add(Int32.MaxValue - 1);
}
}
else if (table.RowCount == 0)
{
rowList = new List <int>(0);
}
else if (groupLinks != null)
{
// If we are grouping, reduce down to only include one row from each
// group.
if (maxColumn == null)
{
rowList = GetTopRowsFromEachGroup();
}
else
{
var colNum = ReferenceTable.FindColumn(maxColumn);
rowList = GetMaxFromEachGroup(colNum);
}
}
else
{
// OPTIMIZATION: This should be optimized. It should be fairly trivial
// to generate a Table implementation that efficiently merges this
// function table with the reference table.
// This means there is no grouping, so merge with entire table,
int rowCount = table.RowCount;
rowList = new List <int>(rowCount);
var en = table.GetEnumerator();
while (en.MoveNext())
{
rowList.Add(en.Current.RowId.RowNumber);
}
}
// Create a virtual table that's the new group table merged with the
// functions in this...
var tabs = new [] { table, this };
var rowSets = new[] { rowList, rowList };
return(new VirtualTable(tabs, rowSets));
}
