上门女婿王子铮和柳萱:大鸟们帮我看看这小段代码~

其中的if检测语句没有用.怎么回事?

set rs=server.CreateObject("adodb.recordset")
rs.Open "select * from musiclist",conn,2,3
dim a(3),b(3),c(3),r,s
for r=0 to 3
a(r)=trim(request.form("songname"&r))
b(r)=trim(request.form("singer"&r))
c(r)=trim(request.form("special"&r))
next
for s=0 to 3
if a(s)="" or b(s)="" or c(s)="" then
response.write"<script LANGUAGE='javascript'>alert('必须全部填写~!');history.go(-1)';</script>"
end if
rs.addnew
rs("songname")=a(s)
rs("singer")=b(s)
rs("special")=c(s)
rs("adddate")=now()
rs.update
next
rs.close
set rs=nothing
我这样写IF还是没起到作用!为什么??

set rs=server.CreateObject("adodb.recordset")
rs.Open "select * from musiclist",conn,2,3
dim a(3),b(3),c(3),r,s
for r=0 to 3
a(r)=trim(request.form("songname"&r))
b(r)=trim(request.form("singer"&r))
c(r)=trim(request.form("special"&r))
if a(s)="" or b(s)="" or c(s)="" then
rs.close
set rs=nothing
response.write"<script LANGUAGE='javascript'>alert('必须全部填写~!');history.go(-1)';</script>"
end if
next
for s=0 to 3
rs.addnew
rs("songname")=a(s)
rs("singer")=b(s)
rs("special")=c(s)
rs("adddate")=now()
rs.update
next
rs.close
set rs=nothing