将 varchar 值 'admin' 转换为数据类型为 int 的列时发生语法错误。

string str = ConfigurationSettings.AppSettings["dsn"];
        SqlConnection cn = new SqlConnection(str);
        cn.Open();
        string mysql = "select * from admin where aid='" + tbx_aid.Text + "'and apassword ='" + tbx_apassword.Text + "'";
        SqlCommand cm =new SqlCommand(mysql,cn);
        SqlDataReader ur =cm.ExecuteReader();
        if (ur.Read())
        {
           
        Session["aid"]= ur["aid"];
        Session["aname"]= ur ["aname"];
        Session["apower"]= ur ["apower"];
        Session["adep"]= ur ["adep"];
        if (Session["apower"]=="1")
        {

            Response.Redirect("admin1.aspx");
        }
         if (Session["apower"]=="2")
        {
            Response.Redirect("kqmanage.aspx");
        }
         if (Session["apower"]=="3")
        {
            Response.Redirect("lr3.aspx");
        }
        label4.Text = "用户名/密码不正确，请重新输入";
         
     } cn.Close();
将 varchar 值 'admin' 转换为数据类型为 int 的列时发生语法错误。 怎么解决啊，请各位帮帮忙