calculating aggregates over row intervals in an update

[Wil Simpson]

what is the best way to calculate: (in the context of an update)
the number of transactions that were entered in the same way as the
current transaction out of the 5 last transactions by the cardholder
(regardless of entry method)

or more generally stated: calculate some aggregate function over a
subset of rows from an interval of rows defined around this row, i.e.
the one being updated

the set-theory happy version:

CREATE TABLE cg (
cardnumber varchar2(16) not null,
entrytype char(1) not null,
chargedate date not null,
NBANAT5#DD0 numeric(7) null) ;

UPDATE cg
SET NBANAT5#DD0
= NVL(( SELECT COUNT(*)
FROM cg t
WHERE t.cardnumber = cg.cardnumber
AND t.entrytype = cg.entrytype
AND ( SELECT COUNT(*)
FROM cg t1
WHERE t1.cardnumber = cg.cardnumber
AND t1.chargedate >= t.chargedate
AND t1.chargedate < cg.chargedate) <= 5
AND t.chargedate <= cg.chargedate ),0) ;

so, for every single row in the transaction history for the
cardholder, it calculates how many rows exist between it and the
current transctions to determine if it is in the last 5 or not. it
works and when each cardholder has a sufficiently small transaction
history then the performance is not TOO bad, but when the transaction
history becomes long it is grotesque. (well, it's grotesque in the
first place, but the response time will change from maybe a minute
over a million rows with small transaction histories to being several
hours over a million rows with long transaction histories)

if it were legal, then the following would perform better, but it
isn't. (no correlated subquery in an in-line view, right?)

UPDATE cg1000
SET NBANAT5#DD0
= NVL(( SELECT count(*)
FROM ( SELECT * from cg t1
where t1.bank_account _number = cg.bank_account _number
and t1.chargedate < cg.chargedate
order by t1.chargedate desc) t
WHERE ROWNUM <= 5
and t.account_type = cg.account_type ),0) ;

conceivable something like

SUM(decode(entr ytype, this.entrytype, 1, 0) OVER (partition by
cardnumber order by chargedate desc rows between 5 preceding and 1
preceding)

would work as well, but i don't see any means of using this in the
context of an udpate statement. (can't use aggregate or analytic
functions in update statements, right?) (and several customers are
using 8i standard which i don't think has analytic functions, right?)

any suggestions?

thank you,
Wil