C# - Non-latin characters doesnt appear properly in database Visual Studio

Question

Here is my code which inserts into database the elements in the textboxes of a dynamic gridview. The code works perfectly but my problem is that the inserted elements that are typed in non-latin characters (greek characters) does not appear propely in database and instead they appear like that:

https://i.stack.imgur.com/pwVTf.jpg

Please can you tell me what to do in order to insert the greek characters properly? Here is the code:

private void InsertRecords(StringCollection sc)
    {
        StringBuilder sb = new StringBuilder(string.Empty);
        string[] splitItems = null;
        const string sqlStatement = "INSERT INTO P_interventions (Date,P_Id,Simeio,Aitio,Etos,Therap) VALUES";
        int id = Convert.ToInt32(Session["pa_id"]);
        foreach (string item in sc)
        {
            if (item.Contains(","))
            {
                splitItems = item.Split(",".ToCharArray());
                sb.AppendFormat("{0}(@Date, @p_id ,'{1}','{2}','{3}','{4}'); ", sqlStatement, splitItems[0], splitItems[1], splitItems[2], splitItems[3]);
            }
        }

        using (SqlConnection connection = new SqlConnection(GetConnectionString()))
        {
            connection.Open();
            using (SqlCommand cmd = new SqlCommand(sb.ToString(), connection))
            {
                cmd.Parameters.AddWithValue("@p_id", id);
                cmd.Parameters.AddWithValue("@Date", DateTime.Now.ToShortDateString());
                cmd.CommandType = CommandType.Text;
                cmd.ExecuteNonQuery();
            }
        }
        lblMessage.ForeColor = System.Drawing.Color.Green;
        lblMessage.Text = "The records have benn inserted successfuly!";
    }

 protected void BtnSave_Click(object sender, EventArgs e)
    {
        //εγχειρήσεις
        int rowIndex = 0;
        StringCollection sc = new StringCollection();
        if (ViewState["CurrentTable"] != null)
        {
            DataTable dtCurrentTable = (DataTable)ViewState["CurrentTable"];
            if (dtCurrentTable.Rows.Count > 0)
            {
                for (int i = 1; i <= dtCurrentTable.Rows.Count; i++)
                {
                    //extract the TextBox values  
                    TextBox box1 = (TextBox)Gridview1.Rows[rowIndex].Cells[1].FindControl("TextBox1");
                    TextBox box2 = (TextBox)Gridview1.Rows[rowIndex].Cells[2].FindControl("TextBox2");
                    TextBox box3 = (TextBox)Gridview1.Rows[rowIndex].Cells[3].FindControl("TextBox3");
                    DropDownList ddl2 = (DropDownList)Gridview1.Rows[rowIndex].Cells[4].FindControl("DropDownList2");
                    //get the values from TextBox and DropDownList  
                    //then add it to the collections with a comma "," as the delimited values  
                    sc.Add(string.Format("{0},{1},{2},{3}", box1.Text, box2.Text, box3.Text, ddl2.SelectedItem.Text));
                    rowIndex++;
                }
                //Call the method for executing inserts  
                InsertRecords(sc);
            }
        }

Answer 1

Since you use nchar fields in your database (as mentioned in a comment), your database already supports Unicode strings. However, you are passing the values you want to insert as non-Unicode string literals in your SQL:

'...'

You need to pass them as Unicode strings:

N'...'

Now don't just put an N in front of your string literals: There's something else you are doing wrong: You are passing user-supplied values by string concatenation, which is a serious security and stability issue. Use parameters instead - you already know how to work with parameters, since you do it for @p_id and @Date. Do the same for your string values. This will also fix the Unicode issue, since AddWithValue defaults to a Unicode parameter type for strings.

Answer 2

I think you have to use the Unicode data types in the database instead of the regular ones (ex:instead of Varchar use NVarchar).

Also in the your code use the N before the string fields Like

 sb.AppendFormat("{0}(@Date, @p_id ,N'{1}',N'{2}',N'{3}',N'{4}'); ", sqlStatement, splitItems[0], splitItems[1], splitItems[2], splitItems[3]);