Help with parameters passing a column to a MySql query

Question

Hi.  I have a function that returns a dictionary with info pulled from a database.  The first parameter of the function is a string of the column to search, the second a string with the value.  I am doing this: 

Dictionary<string, string> getData(string indexfield, string indexvalue) {
  using (MySqlConnection DB = getConnection()) {
    using (MySqlCommand cmd = new MySqlCommand("SELECT * FROM customers WHERE ?if = ?iv", DB) {
      DB.Open();
      cmd.Parameters.AddWithValue("?if", indexfield);
      cmd.Parameters.AddWithValue("?iv", indexvalue);
      using (MySqlDataReader RS = cmd.ExecuteReader()) {
        DataTable schemaTable = RS.GetSchemaTable();
        if (!RS.HasRows) { MessageBox.Show("debug"); return ret; }
        while (RS.Read()) {
          foreach (DataRow fld in schemaTable.Rows) {
            ret.Add(fld["ColumnName"].ToString(), RS[fld["ColumnName"].ToString()].ToString());
          }
        }
      }
      DB.Close();
    }
  }

 When I run that, I get the "debug" messagebox indicating no rows.  I enabled the general log in MySQL, and I see this when passing field cid and value 5:

 

SELECT * FROM customers WHERE 'cid' = '5'

 

I copied that and ran the query, it failed.  Once I made it cid instead of 'cid', it worked fine.  Why is C# adding quotes around my field?  Is it because the variable being passed to cmd.Parameters.AddWithValue is a string?  Is there any way to stop that?