public override SqlObject VisitSelect_list_spec([NotNull] sqlParser.Select_list_specContext context)
        {
            Contract.Requires(context != null);

            List <SqlSelectItem> sqlSelectItems = new List <SqlSelectItem>();

            foreach (sqlParser.Select_itemContext selectItemContext in context.select_item())
            {
                SqlSelectItem selectItem = (SqlSelectItem)this.Visit(selectItemContext);
                sqlSelectItems.Add(selectItem);
            }

            return(SqlSelectListSpec.Create(sqlSelectItems.ToImmutableArray()));
        }