Decreasing a value with a named parameter doesn't change said value

Question

I want to decrease my urunadedi value in an Access database. I have the following code:

cmd2.Connection = con;
cmd2.Parameters.AddWithValue(\"@uruni         


        

Answer 1

Microsoft OLEDB ignores parameter names and only pays attention to the order in which the parameters appear in the CommandText. So, for

cmd2.CommandText = @"UPDATE Table1
                     SET urunadedi=urunadedi-@hesaplam
                     WHERE urunadi=@urunid";

we need to add the @hesaplam parameter first since it appears first in the CommandText

cmd2.Parameters.AddWithValue("@hesaplam", Convert.ToInt64(textBox2.Text));
cmd2.Parameters.AddWithValue("@urunid", Convert.ToInt64(textBox1.Text));

Note also that because the OLEDB parameter names are ignored it is quite common to see the question mark (?) being used as the parameter placeholder:

cmd2.CommandText = @"UPDATE Table1
                     SET urunadedi=urunadedi-?
                     WHERE urunadi=?";
cmd2.Parameters.AddWithValue("?", Convert.ToInt64(textBox2.Text));  // @hesaplam
cmd2.Parameters.AddWithValue("?", Convert.ToInt64(textBox1.Text));  // @urunid