How to take a value from a database? Must declare the scalar variable “@ID1”

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 :D

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.

Answer 2

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.aspx

SqlCommand has a Parameters collection.

see also: http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlcommand.parameters.aspx

quote:

using (SqlConnection connection = new SqlConnection(connectionString))
{
    SqlCommand command = new SqlCommand(commandText, connection);
    command.Parameters.Add("@ID", SqlDbType.Int);
    command.Parameters["@ID"].Value = customerID;

    // Use AddWithValue to assign Demographics.
    // SQL Server will implicitly convert strings into XML.
    command.Parameters.AddWithValue("@demographics", demoXml);

    try
    {
        connection.Open();
        Int32 rowsAffected = command.ExecuteNonQuery();
        Console.WriteLine("RowsAffected: {0}", rowsAffected);
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

Answer 3

You need to pass in the value of the parameter. Add this line right after you initialize the dataCommand variable:

dataCommand.Parameters.Add("@ID", ID1);

Answer 4

You need to add a parameter to the DataCommand because you said there's one.

ID = @ID1

tells the server to puck up the data from the parameter @ID1. Then you don't declare a parameter.

Check the Parameters collection on the DataCommand object. Add a parameter.

Answer 5

You have to add the Parameter to the SqlCommand.Parameters collection because you have @ID1 within your query.

do that before ExecuteScalar

dataCommand.Parameters.Add(new SqlParameter("@ID1", ID1));

complete solution

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.Add(new SqlParameter("@ID1", ID1));

        cn.Open();

        var = Convert.ToString(dataCommand.ExecuteScalar());

        label3.Text = var;
    }
}

hope this helps