为什么输入重复的用户名也不提示重复啊该怎么处理

为什么输入重复的用户名也不提示重复啊
Do While rs.EOF
  rs.Open "select username from information ", cn, adOpenStatic, adLockOptimistic
  If txtusername.Text = rs.Fields("username") Then
  Label21.ForeColor = vbRed
  Label21.Caption = "用户名已存在"
  MsgBox "用户名已存在！", vbInformation, "用户错误"
  GoTo aa
  Else
  GoTo bb
  End If
  Loop

------解决方案--------------------

VB code

'判断输入的用户是否存在
strsql=" SELECT username FROM information WHERE username='"& trim(txtusername.text) &"'"
if rs.state<>adstateclosed then rs.close
rs.open strsql,cn,adopenkeyset,adlockreadonly
if rs.recordcount>0 then
    label21.forecolor=vbred
    label21.capiton="用户名已经在在"
    label21.refresh
    msgbox "用户名已经在在!",48,"错误"
    goto aa
else
    goto bb
end if