How to use Join or Aggregate in SQL query

Question

When performing the query in a given table, numOrc is a list that may contain one or more values.

So I needed to concatenate these values into one string, using ; as a limiter.

So I tried:

var model = (from s in db.Vendas_pedidos
                     join p in db.Cliente_contatos on s.idContato equals p.id_cliente_contato into _p
                     from p in _p.DefaultIfEmpty()
                     join t in (
                             from t1 in db.Vendas_itens
                             group t1 by t1.numeroPedido into g
                             select new
                             {
                                 numeroPed = g.Key,
                                 valorTotal = g.Sum(x => x.valortotal),
                                 maxStatus = g.Max(x => x.status),
                                 tipoMaterial = g.Max(x => x.tipoElemento),
                                 numOrc = g.Select(x => x.numOrc)
                             }
                             ) on s.id equals t.numeroPed
                     where s.idCliente == codCliente
                     select new
                     {
                         id = s.id,
                         dataCad = s.dataEmissao,
                         contato = (p.nome + " " + p.sobrenome),
                         valorTotal = ("R$ " + t.valorTotal.ToString()),
                         dataSolicCotacao = s.dataSolicCotacao,
                         status = t.maxStatus,
                         tipoMaterial = (t.tipoMaterial.ToString().Equals("5") ? "Serviço" : "Venda").ToString(),
                         numOrc = t.numOrc.ToList().Aggregate((a, b) => a + ";" + b)
                     }).OrderByDescending(x => x.id).ToList();

But when executing the error is returned:

Answer 1

Why not do:

numOrc = string.Join(";", t.numOrc)

instead of:

numOrc = t.numOrc.ToList().Aggregate((a, b) => a + ";" + b)

?