请教一个数据相加的问题

<%
set conn=server.createobject("adodb.connection")
conn.open "driver={microsoft access driver (*.mdb)};dbq="&server.mappath("dat/tj.mdb")
exec="select * from sj where rq="&request.form("rq")
set rs=server.createobject("adodb.recordset")
rs.open exec,conn,1,3
t1=rs("t2")+rs("t3")
rs("t1")=request.form("t1")
response.write rs("t2")
response.write rs("t3")
response.write rs("t1")
response.write rs("rq")
rs.update
rs.close
set rs=nothing
conn.close
set conn=nothing
%>
这段代码,rq=1,t2=2,t3=3,只有t1显示不出来,请问哪错了?