How do I join two results of a query?

How about joining through the sql query itself using UNION :

select id, nome, email from funcionario
union
select id, nome, email from fornecedor

In your case it would look like this:

string sql_todos = "select id, nome, email from funcionario " +
                   "union "+
                   "select id, nome, email from fornecedor";

@Ecil's response is adequate, but I add the use of UNION ALL .

What is the difference between UNION and UNION ALL ?

• UNION makes a kind of DISTINCT , inhibiting repeated results
• UNION ALL brings all results, even those with repeated values

Is there any advantage in UNION ALL ? In theory, it is more efficient by not applying DISTINCT , that is, by not comparing the values of the registers.

So just a simple change:

string sql_todos = "select id, nome, email from funcionario " +
               "union all "+
               "select id, nome, email from fornecedor";

This concept applies at least to SQL Server, Oracle, MySQL and PostgreSQL.

In theory, you just have to repeat the process of reopening the connection, running the other query, and passing the loopback by adding the results of your second query.

string sql_funcionario = "select id, nome, email from funcionario";
string sql_fornecedor = "select id, nome, email from fornecedor";

var conexao = new SqlConnection("string de conexão");


MalaDireta m = new MalaDireta();
var comando = new SqlCommand(sql_funcionario, conexao);

try
{
   conexao.Open();

   // como eu monto meu comando com as duas queries?

   var dataReader = comando.ExecuteReader();
   while (dataReader.Read())
   {

      m.Nome = dataReader["nome"];
      m.Email = dataReader["email"];

      resultado.Add(m);
   }
}
catch
{
}
finally
{
   conexao.Close();
}

var comando = new SqlCommand(sql_fornecedor, conexao);

try
{
   conexao.Open();

   // como eu monto meu comando com as duas queries?

   var dataReader = comando.ExecuteReader();
   while (dataReader.Read())
   {

      m.Nome = dataReader["nome"];
      m.Email = dataReader["email"];

      resultado.Add(m);
   }
}
catch
{
}
finally
{
   conexao.Close();
}

There are two ways:

var query = "select id, nome, email from funcionario union select id, nome, email from fornecedor";

    var comando = new SqlCommand(string.Concat(sql_funcionario, ";", sql_fornecedor), conexao);
    var dataReader = comando.ExecuteReader();
    while (dataReader.NextResult()) {
        while (dataReader.Read()) {
            MalaDireta m = new MalaDireta();
            m.Nome = dataReader["nome"];
            m.Email = dataReader["email"];

            resultado.Add(m);
        }
    }

Dear, even if some hidden magic can be put together to bring the two readers together for readability, I only see two options: