Mengambil ID yang terakhir dimasukkan menggunakan scope_Identity()

Anda tidak boleh membagi kueri menjadi dua kueri. Anda harus memilih/mengatur hasilnya dalam kueri penyisipan.

Saya membuat contoh untuk Anda:

Metode pertama mengembalikan nilai tunggal dengan menggunakan select

private void Method1()
{
    string sEmail = "[email protected]";
    string passwordHash = "#[email protected]#[email protected]!#@[email protected]#!#@$!#@$!";
    string salt = "????";
    string sName = "John";

    using (SqlConnection sqlConnection = new SqlConnection(_connectionString))
        try
        {
            sqlConnection.Open();

            string insertStatement = "INSERT INTO [User] "
                                        + "(email, hash, salt, name) "
                                        + "VALUES (@email, @hash, @salt, @name)"

                                        + "SELECT SCOPE_IDENTITY()";

            using (SqlCommand insertCommand = new SqlCommand(insertStatement, sqlConnection))
            {

                insertCommand.Parameters.Add("@email", SqlDbType.VarChar, 50).Value = sEmail;
                insertCommand.Parameters.Add("@hash", SqlDbType.VarChar, 50).Value = passwordHash;
                insertCommand.Parameters.Add("@salt", SqlDbType.VarChar, 50).Value = salt;
                insertCommand.Parameters.Add("@name", SqlDbType.VarChar, 50).Value = sName;


                int userId = Convert.ToInt32(insertCommand.ExecuteScalar());
                Trace.WriteLine("User created with id: " + userId);
            }
        }

        catch (SqlException ex)
        {
            Trace.WriteLine(ex.Message);
            //lblMessage.Text = ex.Message;
        }
}

Metode kedua adalah mendefinisikan parameter keluaran, dengan cara ini Anda dapat mengembalikan beberapa nilai.

private void Method2()
{
    string sEmail = "[email protected]";
    string passwordHash = "#[email protected]#[email protected]!#@[email protected]#!#@$!#@$!";
    string salt = "????";
    string sName = "John";

    using (SqlConnection sqlConnection = new SqlConnection(_connectionString))
        try
        {
            sqlConnection.Open();

            string insertStatement = "INSERT INTO [User] "
                                        + "(email, hash, salt, name) "
                                        + "VALUES (@email, @hash, @salt, @name)"

                                        + "SET @user_id = SCOPE_IDENTITY()";

            using (SqlCommand insertCommand = new SqlCommand(insertStatement, sqlConnection))
            {

                insertCommand.Parameters.Add("@email", SqlDbType.VarChar, 50).Value = sEmail;
                insertCommand.Parameters.Add("@hash", SqlDbType.VarChar, 50).Value = passwordHash;
                insertCommand.Parameters.Add("@salt", SqlDbType.VarChar, 50).Value = salt;
                insertCommand.Parameters.Add("@name", SqlDbType.VarChar, 50).Value = sName;

                insertCommand.Parameters.Add("@user_id", SqlDbType.Int).Direction = ParameterDirection.Output;

                insertCommand.ExecuteNonQuery();

                int userId = Convert.ToInt32(insertCommand.Parameters["@user_id"].Value);
                Trace.WriteLine("User created with id: " + userId);
            }
        }

        catch (SqlException ex)
        {
            Trace.WriteLine(ex.Message);
            //lblMessage.Text = ex.Message;
        }
}

Yang terbaik yang dapat Anda lakukan adalah, jika kuerinya statis, menempatkan kueri ini dalam prosedur tersimpan. Ini akan mempercepat kueri.