public static ITable GroupConcat(QueryProcessor processor, bool distinct, ITable group, Expression[] args)
{
// The output string
StringBuilder return_string = new StringBuilder();
// Find the distinct subset of group
if (distinct)
group = processor.DistinctSubset(group, args);
// Push the group table onto the processor stack
processor.PushTable(group);
// Iterator over the group
IRowCursor i = group.GetRowCursor();
bool first = true;
while (i.MoveNext()) {
RowId rowid = i.Current;
processor.UpdateTableRow(rowid);
foreach (Expression op in args) {
ITable val = processor.Execute(op);
SqlObject ob = QueryProcessor.Result(val)[0];
if (!ob.IsNull) {
if (!first) {
return_string.Append(", ");
}
return_string.Append(SqlValue.FromObject(ob.Value).ToString());
first = false;
}
}
}
// Pop the table and return the result
processor.PopTable();
return QueryProcessor.ResultTable(new SqlObject(return_string.ToString()));
}
private static ITable ProcessAggregate(QueryProcessor processor, bool distinct, ITable group, Expression[] args, IAggregateInspector aggregator)
{
// Qualify the return type of the parameter
SqlType type = processor.GetExpressionType(group, args[0]);
// If an empty group
if (group.RowCount == 0) {
// Null return type if group is empty,
return QueryProcessor.ResultTable(SqlObject.MakeNull(type));
}
// Find the distinct subset of group
if (distinct)
group = processor.DistinctSubset(group, args);
// Push the group table onto the processor stack
processor.PushTable(group);
// Scan the group table, returning null on a null value
IRowCursor i = group.GetRowCursor();
while (i.MoveNext()) {
RowId rowid = i.Current;
processor.UpdateTableRow(rowid);
ITable val = processor.Execute(args[0]);
SqlObject ob = QueryProcessor.Result(val)[0];
// If we hit a null value, we ignore it. SQL-92 apparently says we
// should generate a warning for nulls that are eliminated by set
// functions.
if (!ob.IsNull) {
aggregator.Accumulate(ob);
}
}
// Pop the table and return the result
processor.PopTable();
SqlObject result = aggregator.Result();
return QueryProcessor.ResultTable(result ?? SqlObject.MakeNull(type));
}