asp中用数据库生成不重复的流水号

代码如下:
'*************************************************
'函数名：getMaxOrder
'作 用：得到最大序列号
'参 数：fieldName ----在序列号表中的字段名
' tableName ----序列号所在表名
' fieldName ----在表中的字段名
'返回值：字段的最大值
'调用函数：idAdd：作用见上
'*************************************************
function getMaxOrder(fieldName,tableName,tableFileName)
dim orderNO,orderRS,testRS
set testRS=Server.CreateObject("ADODB.recordset")
set orderRS=Server.CreateObject("ADODB.recordset")
firstNO=year(date)&right(("0"&month(date)),2)
orderSQL="select * from fieldMaxValue where fieldName='"&fieldName&"'"
orderRS.open orderSQL,conn,3,2
if not orderRS.eof then
orderRS("fieldMaxValue")=orderRS("fieldMaxValue")
orderNO=orderRS("fieldMaxValue")
if left(orderNO,6)=firstNO then
orderNO=idAdd(orderNO)
else
orderNO=firstNO&"00001"
end if
else
orderRS.addnew
orderRS("fieldName")=fieldName
orderNO=firstNO&"00001"
end if
testRS.open "select max("&tableFileName&") from "&tableName&" where "&tableFileName&" like '"&firstNO&"%'",conn,1,2
if (not testRS.eof) and testRS(0).value>orderNO then
orderNO=idAdd(testRS(0).value)
end if
testRS.close
set testRS=nothing
orderRS("fieldMaxValue")=orderNO
orderRS.update
orderRS.close
set orderRS=nothing
getMaxOrder=orderNO
end function

'*************************************************
'函数名：idAdd
'作 用：用来增加一：比如idAdd("5")="6",idAdd("L99")="M00"，idAdd("!")="!1"
' 如果是数字就到9后进位,如果是小写字母到期z后进位
' 如果是大写字母到Z后进位，其它在后面加一个1
'参 数：id ----需来增加的数
'返回值：增加后的数
'调用函数：addOne 一个数增加一 AddOne("5")="6",Add(9)="0",AddOne("a")="b",
' AddOne("z")="a",AddOne("A")="B",AddOne("Z")="A"
'*************************************************
Function AddOne(first)
Dim tempfirst
AddOne = first
intfirst = Asc(first)
If (intfirst >= 48 And intfirst < 57) Or (intfirst >= 65 And intfirst < 90) Or (intfirst >= 97 And intfirst < 122) Then
AddOne = Chr(intfirst + 1)
Exit Function
End If
If (intfirst = 57) Then
AddOne = "0"
Exit Function
End If
If (intfirst = 90) Then
AddOne = "A"
Exit Function
End If
If (intfirst = 122) Then
AddOne = "a"
Exit Function
End If
End Function
Function idAdd(id)
Dim fornt, back, strFind, strBackFind, idLen, tempid
if id="" or isNull(id) then
iddAdd=1
exit Function
end if
tempid = id
idLen = Len(id)
For i = 1 To idLen
fornt = Left(id, idLen - i)
back = Right(id, i - 1)
strFind = Mid(id, idLen + 1 - i, 1)
strBackFind = AddOne(strFind)
id = fornt & strBackFind & back
If strFind < strBackFind Then
Exit For
End If
If strFind > strBackFind Then
If i = idLen Then
id = id & "1"
Else
If Mid(id, idLen - i, 1) = AddOne(Mid(id, idLen - i, 1)) Then
id = fornt & strBackFind & back & "1"
Exit For
End If
End If
End If
Next
If id = tempid Then
id = id & "1"
End If
idAdd = id
End Function

'调用示例
serviceNO=getMaxOrder("serviceNO","service","serviceNO")

'其中保存所有字段流水号最大值的表的结构为:
表名:fieldMaxValue
字段
id fieldName fieldMaxValue