Dim tablename As String
        tablename = "userid"
        searchSQL = "SELECT  用户名,密码 from userid where (用户名 = '" & TextBox1.Text & "') "
        Try
            ExecuteSQL(searchSQL, tablename) '查询函数
            If myrow.Item(1) = TextBox2.Text Then
                Dim newfrmmain As New frmmain'如果正解则打开主frmmain
                               Me.Close()

            Else
                Exit Sub
            End If
        Catch
            MsgBox("没有该用户", vbOKOnly + vbExclamation, "警告")
        End Try

SqlConnection myconnection =new SqlConnection(server=服务器名;uid=用户;pwd=密码 ;database=数据库名);
myconnection.Open();
DataSet ds=new DataSet();
SqlDataAdapter da=new SqlDataAdapter("select * from 用户信息表 where 用户名='"+txtUserName.Text.ToString()+"' ",myconnection);
da.Fill(ds,"UserNameView");
if(ds.Tables["UserNameView"].Rows.Count!=0)
  {Response.Write("该用户名已有人使用,请重新输入用户名");
   UserName.Text="";
  }
  else
  {
    Response.Write("该用户名没有人使用过，您可以使用！");
  }
myconnection.Close();