新手求助避免向数据库插入重复数据的SQL语句 - 编程论坛

本人超级菜鸟，通过视频教材用DW做了一个简单的网站，但让我用SQL语句自己写程序真的还是搞不太懂，以下是我的一个后台添加新用户的页面，哪位大侠能帮加段SQL语句进去，目的是帮我检测数据库中用户名列（gname）如果有重复则返回重输，否则就添加成功。万分感谢！

程序代码：

<%@LANGUAGE="VBSCRIPT"%>
<% If Session("jb")<>1 Then %>
<script>
alert("权限不够！")
window.location.href="index.asp"
</script>
<% End If %>

<%
' *** Restrict Access To Page: Grant or deny access to this page
MM_authorizedUsers=""
MM_authFailedURL="errro3.asp"
MM_grantAccess=false
If Session("MM_Username") <> "" Then
  If (true Or CStr(Session("MM_UserAuthorization"))="") Or _
         (InStr(1,MM_authorizedUsers,Session("MM_UserAuthorization"))>=1) Then
    MM_grantAccess = true
  End If
End If
If Not MM_grantAccess Then
  MM_qsChar = "?"
  If (InStr(1,MM_authFailedURL,"?") >= 1) Then MM_qsChar = "&"
  MM_referrer = Request.ServerVariables("URL")
  if (Len(Request.QueryString()) > 0) Then MM_referrer = MM_referrer & "?" & Request.QueryString()
  MM_authFailedURL = MM_authFailedURL & MM_qsChar & "accessdenied=" & Server.URLEncode(MM_referrer)
  Response.Redirect(MM_authFailedURL)
End If
%>
<%
Dim MM_editAction
MM_editAction = CStr(Request.ServerVariables("SCRIPT_NAME"))
If (Request.QueryString <> "") Then
  MM_editAction = MM_editAction & "?" & Server.HTMLEncode(Request.QueryString)
End If

' boolean to abort record edit
Dim MM_abortEdit
MM_abortEdit = false
%>
<%
' IIf implementation
Function MM_IIf(condition, ifTrue, ifFalse)
  If condition = "" Then
    MM_IIf = ifFalse
  Else
    MM_IIf = ifTrue
  End If
End Function
%>
<%
If (CStr(Request("MM_insert")) = "form1") Then
  If (Not MM_abortEdit) Then
    ' execute the insert
    Dim MM_editCmd

    Set MM_editCmd = Server.CreateObject ("")
    MM_editCmd.ActiveConnection = MM_conn_STRING
    MM_ = "INSERT INTO dbo.g_glbiao (gname, gpass, gjb, xm, dm, jh, tel) VALUES (?, ?, ?, ?, ?, ?, ?)"
    MM_editCmd.Prepared = true
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param1", 202, 1, 50, Request.Form("gname")) ' adVarWChar
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param2", 202, 1, 50, Request.Form("gpass")) ' adVarWChar
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param3", 5, 1, -1, MM_IIF(Request.Form("gjb"), Request.Form("gjb"), null)) ' adDouble
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param4", 202, 1, 50, Request.Form("xm")) ' adVarWChar
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param5", 202, 1, 50, Request.Form("dm")) ' adVarWChar
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param6", 202, 1, 50, Request.Form("jh")) ' adVarWChar
    MM_editCmd.Parameters.Append MM_editCmd.CreateParameter("param7", 202, 1, 50, Request.Form("tel")) ' adVarWChar
    MM_editCmd.Execute
    MM_editCmd.ActiveConnection.Close

    ' append the query string to the redirect URL
    Dim MM_editRedirectUrl
    MM_editRedirectUrl = "htgl.asp"
    If (Request.QueryString <> "") Then
      If (InStr(1, MM_editRedirectUrl, "?", vbTextCompare) = 0) Then
        MM_editRedirectUrl = MM_editRedirectUrl & "?" & Request.QueryString
      Else
        MM_editRedirectUrl = MM_editRedirectUrl & "&" & Request.QueryString
      End If
    End If
    Response.Redirect(MM_editRedirectUrl)
  End If
End If
%>
<%
Dim u
Dim u_cmd
Dim u_numRows

Set u_cmd = Server.CreateObject ("")
u_cmd.ActiveConnection = MM_conn_STRING
u_ = "SELECT * FROM dbo.g_glbiao ORDER BY t DESC"
u_cmd.Prepared = true

Set u = u_cmd.Execute
u_numRows = 0
%>
<%
Dim Repeat1__numRows
Dim Repeat1__index

Repeat1__numRows = -1
Repeat1__index = 0
u_numRows = u_numRows + Repeat1__numRows
%>

<%
'  *** Recordset Stats, Move To Record, and Go To Record: declare stats variables

Dim u_total
Dim u_first
Dim u_last

' set the record count
u_total = u.RecordCount

' set the number of rows displayed on this page
If (u_numRows < 0) Then
  u_numRows = u_total
Elseif (u_numRows = 0) Then
  u_numRows = 1
End If

' set the first and last displayed record
u_first = 1
u_last  = u_first + u_numRows - 1

' if we have the correct record count, check the other stats
If (u_total <> -1) Then
  If (u_first > u_total) Then
    u_first = u_total
  End If
  If (u_last > u_total) Then
    u_last = u_total
  End If
  If (u_numRows > u_total) Then
    u_numRows = u_total
  End If
End If
%>

<%
' *** Recordset Stats: if we don't know the record count, manually count them

If (u_total = -1) Then

  ' count the total records by iterating through the recordset
  u_total=0
  While (Not u.EOF)
    u_total = u_total + 1
    u.MoveNext
  Wend

  ' reset the cursor to the beginning
  If (u.CursorType > 0) Then
    u.MoveFirst
  Else
    u.Requery
  End If

  ' set the number of rows displayed on this page
  If (u_numRows < 0 Or u_numRows > u_total) Then
    u_numRows = u_total
  End If

  ' set the first and last displayed record
  u_first = 1
  u_last = u_first + u_numRows - 1

  If (u_first > u_total) Then
    u_first = u_total
  End If
  If (u_last > u_total) Then
    u_last = u_total
  End If

End If
%>
<%
Dim MM_paramName
%>
<%
' *** Go To Record and Move To Record: create strings for maintaining URL and Form parameters

Dim MM_keepNone
Dim MM_keepURL
Dim MM_keepForm
Dim MM_keepBoth

Dim MM_removeList
Dim MM_item
Dim MM_nextItem

' create the list of parameters which should not be maintained
MM_removeList = "&index="
If (MM_paramName <> "") Then
  MM_removeList = MM_removeList & "&" & MM_paramName & "="
End If

MM_keepURL=""
MM_keepForm=""
MM_keepBoth=""
MM_keepNone=""

' add the URL parameters to the MM_keepURL string
For Each MM_item In Request.QueryString
  MM_nextItem = "&" & MM_item & "="
  If (InStr(1,MM_removeList,MM_nextItem,1) = 0) Then
    MM_keepURL = MM_keepURL & MM_nextItem & Server.URLencode(Request.QueryString(MM_item))
  End If
Next

' add the Form variables to the MM_keepForm string
For Each MM_item In Request.Form
  MM_nextItem = "&" & MM_item & "="
  If (InStr(1,MM_removeList,MM_nextItem,1) = 0) Then
    MM_keepForm = MM_keepForm & MM_nextItem & Server.URLencode(Request.Form(MM_item))
  End If
Next

' create the Form + URL string and remove the intial '&' from each of the strings
MM_keepBoth = MM_keepURL & MM_keepForm
If (MM_keepBoth <> "") Then
  MM_keepBoth = Right(MM_keepBoth, Len(MM_keepBoth) - 1)
End If
If (MM_keepURL <> "")  Then
  MM_keepURL  = Right(MM_keepURL, Len(MM_keepURL) - 1)
End If
If (MM_keepForm <> "") Then
  MM_keepForm = Right(MM_keepForm, Len(MM_keepForm) - 1)
End If

' a utility function used for adding additional parameters to these strings
Function MM_joinChar(firstItem)
  If (firstItem <> "") Then
    MM_joinChar = "&"
  Else
    MM_joinChar = ""
  End If
End Function
%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.>
<html xmlns="http://www.>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title></title>
<link href="css.css" rel="stylesheet" type="text/css" />
<style type="text/css">

</style>

</head>

<body>

<table width="800" border="0" align="center" cellpadding="6" cellspacing="0">
  <tr valign="top">
    <td bordercolor="#FFFFFF" bgcolor="#003399" id="objFiles"><span class="STYLE4">添加新的管理员</span></td>
  </tr>
  <tr valign="top">
    <td bordercolor="#FFFFFF" bgcolor="#FFCC99" id="objFiles3"><form action="<%=MM_editAction%>" method="post" name="form1" id="form1">
        <table align="center">
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">用户名</td>
            <td><input type="text" name="gname" value="" size="32" />
            <div id="gname1"></div>           </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">密码</td>
            <td><input type="text" name="gpass" value="" size="32" />            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">管理级别</td>
            <td><select name="gjb" id="gjb">
              <option value="3">普通用户</option>
              <option value="2">高级用户</option>
              <option value="1">系统管理员</option>
            </select>            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">姓名</td>
            <td><input type="text" name="xm" value="" size="32" />            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">代码</td>
            <td><input type="text" name="dm" value="" size="32" />            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">联系电话</td>
            <td><input type="text" name="tel" value="" size="32" />            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap">备注</td>
            <td><input type="text" name="jh" value="" size="32" />            </td>
          </tr>
          <tr valign="baseline">
            <td align="right" nowrap="nowrap"> </td>
            <td><input type="submit" value="添加新的管理员" /></td>
          </tr>
        </table>
        <input type="hidden" name="MM_insert" value="form1" />
    </form>
    </td>
  </tr>
</table>

</body>
</html>
<%
u.Close()
Set u = Nothing
%>