Column 'Value' does not belong to table

Question

I have stored some number data under column name Value in the tblV table of my database. I want to put the data from that column Value into textbox1. But whenever I click the button it shows Column 'Value' does not belong to table error even though there is column Value in the table. What is causing this problem?

The first one is class and second one is the code on button click event.

 public DataTable GetMaxno(decimal Licenseno)
    {
        SqlConnection con = new SqlConnection("Data Source=(LocalDB)\\MSSQLLocalDB; Integrated Security=True; Initial Catalog=sudipDB;");
        string sql = "select Max(Value) from tblv where Licenseno=@licenseno";
        SqlCommand cmd = new SqlCommand(sql, con);
        cmd.Parameters.AddWithValue("@Licenseno",Licenseno );
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataTable DT = new DataTable();
        da.Fill(DT);
        return DT;
    }



 tryv tv = new tryv();
    private void button1_Click(object sender, EventArgs e)
    {
        DataTable dt = tv.GetMaxno(Convert.ToDecimal(textBox2.Text));
        if (dt.Rows.Count > 0)
        {
            textBox1.Text= dt.Rows[0]["Value"].ToString();
        }
    }

Answer 1

Reason might be that your query does not return any aliases as Value. You can solve this with select Max(Value) as Value but instead of that, use ExecuteScalar instead which is exactly what you want. It returns first column of the first row.

A few things more;

• Use using statement to dispose your connection and command.
• Do not use AddWithValue. It may generate unexpected and surprising result sometimes. Use Add method overloads to specify your parameter type and it's size.

public int GetMaxno(decimal Licenseno)
{
     using(var con = new SqlConnection("Data Source=(LocalDB)\\MSSQLLocalDB; Integrated Security=True; Initial Catalog=sudipDB;")
     using(var cmd = con.CreateCommand())
     {
        cmd.CommandText = "select Max(Value) from tblv where Licenseno = @licenseno";
        cmd.Parameters.Add("@licenseno", SqlDbType.Decimal).Value = Licenseno;
        con.Open();
        return (int)cmd.ExecuteScalar();
     }
}

Then you can do;

textBox1.Text = tv.GetMaxno(Convert.ToDecimal(textBox2.Text)).ToString();

Answer 2

try

string sql = "select Max(Value) as Value from tblv where Licenseno=@licenseno";