public SelectExpression(QualifiedName selection, Name alias)
{
if (selection == null)
throw new ArgumentNullException("selection", "selection is null.");
this.selection = selection;
this.alias = alias;
}
public SelectExpression As(Name alias)
{
if (this.alias != null)
throw new InvalidOperationException("Alias already set.");
var clone = this.Clone();
clone.alias = alias;
return clone;
}