至少一个参数没有被指定值。

  string s = "";
        string str = "select xingming,dianhua,zhuti,neirong from youke";
        OleDbConnection cn = new OleDbConnection(System.Configuration.ConfigurationManager.AppSettings["SQLConnString"].ToString());
        OleDbDataAdapter da = new OleDbDataAdapter(str, cn);
        DataSet ds = new DataSet();
        da.Fill(ds);
        int ret = 0;
        for (int i = 0; i <= youkexinxi.count() - 1; i++)
        {
            string s1 = ds.Tables[0].Rows[i]["zhuti "].ToString();
            if (zhuti == s1)
                ret = 1;
        }
        if (ret == 1)
        {
            s = "";
        }
        else
        {
            s = "没有该主题";
        }
        return s;