private OrderByClause BuildNestedOrderBy(SelectExpression select, OrderByClause orderBy)
{
if (orderBy == null)
return null;
var newOrderBy = new OrderByClause(BuildNestedOrderBy(select, orderBy.SecondarySortingClause));
var columns = orderBy.SortColumns;
var unmatchedColumns = new List<Expression>();
foreach (var col in columns)
{
Expression expr = select.TryFindColumn(col.Item1);
if (expr == null)
expr = select.AddUnmappedColumn(col.Item1);
newOrderBy.AppendColumn(Tuple.Create(expr, col.Item2));
}
return newOrderBy;
}
