All records updated with same value when updating database Record

Question

I updated sql data base using c# text box but all records updated with same value what I entered in that text box. where I did wrong.

Below My code

private void btnsave_Click(object sender, EventArgs e)
{
    try
    {
        string connectionString = (@"Data Source = M2\SQL2016; Initial Catalog = inventoryDB; Integrated Security = True");

        using (SqlConnection conn = new SqlConnection(connectionString))
        {
            conn.Open();
            using (SqlCommand cmd =
                    new SqlCommand("UPDATE companyDB SET compname=@label3", conn))
            {
                cmd.Parameters.AddWithValue("@label3", cmpname.Text);
                int rows = cmd.ExecuteNonQuery();
            }


        }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Not Updated");
    }

Answer 1

You should set the where clause here to filter what records should be updated. The WHERE clause is used to extract only those records that fulfill a specified criterion. See the following example which filters based on id column:

new SqlCommand("UPDATE companyDB SET compname=@label3 where id = @id", conn))

And:

cmd.Parameters.AddWithValue("@id", id.Text);

Although specify the type directly and use the Value property is more better than AddWithValue :

cmd.Parameters.Add("@label3", SqlDbType.VarChar).Value = cmpname.Text;

Also check here: Can we stop using AddWithValue() already?