Question

  public partial class Form3 : Form
  {       
    string var;
    int ID1;

    private void button1_Click(object sender, EventArgs e)
    {
        ID1 = int.Parse(textBox1.Text);
        SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\asp\Desktop\DatabasesPractice\DatabasesPractice\soccer.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True");
        SqlCommand dataCommand = new SqlCommand("SELECT Name FROM team WHERE ID = @ID1", cn);

        cn.Open();
        var = Convert.ToString(dataCommand.ExecuteScalar());
        label3.Text = var;

    }
 }

It gives me an error saying I must declare the scalar variable @ID, I’m searching everywhere and can’t get a solution for my specific case.

Thanks for the help people! your solutions worked 😀

Answer 1

public partial class Form3 : Form 
{        
    string var; 
    int ID1; 

private void button1_Click(object sender, EventArgs e) 
{ 
    ID1 = int.Parse(textBox1.Text); 
    SqlConnection cn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\Users\asp\Desktop\DatabasesPractice\DatabasesPractice\soccer.mdf;Integrated Security=True;Connect Timeout=30;User Instance=True"); 
    SqlCommand dataCommand = new SqlCommand("SELECT Name FROM team WHERE ID = @ID1", cn); 
    dataCommand.Parameters.AddWithValue("@ID1", ID1); // this is the new line of code

    cn.Open(); 
    var = Convert.ToString(dataCommand.ExecuteScalar()); 
    label3.Text = var; 

} 

}

See above, I have added dataCommand.Parameters.AddWithValue("@ID1", ID1);. What that does is defines your parameter for your SQL query and passes it the value. I assumed that you’d want the variable ID1 to be the value of your SQL parameter @ID1.