Help in subquery update

Question

I am trying to do the oracle version, thats where I kind of got stuck, what I have to do in the external where clause. Any help is appreciated.
Thanks
/* sybase version
update sale_upgrades_temp
set a.exchangeRate = b.conversionRate
from sale_upgrades_temp a, CurrencyConversion b
where a.chargeCurrency = b.name
and (convert(datetime,convert(varchar(11),a.workCompleted,101))
>= b.effectivePeriodStartDate)
and (convert(datetime,convert(varchar(11),a.workCompleted,101))
<= b.effectivePeriodEndDate
OR b.effectivePeriodEndDate is null)
--trifleet_hyperion_user.
update sale_upgrades_temp
set exchangeRate =(select b.conversionRate
from CurrencyConversion b
where sale_upgrades_temp.chargeCurrency = b.name
and ( to_date(sale_upgrades_temp.workCompleted)
>= b.effectivePeriodStartDate)
and (to_date(sale_upgrades_temp.workCompleted))
<= b.effectivePeriodEndDate
OR b.effectivePeriodEndDate is null))
where (sale_upgrades_temp.chargeCurrency, sale_upgrades_temp.workCompleted)
in (select

Answer 1

I tried this and obviously I got the error, as subquery retursn morethan one row as my external where clause does not have any filter condition. Could some shed some light on this ?
update sale_upgrades_temp
set exchangeRate =(select b.conversionRate
from CurrencyConversion b
where sale_upgrades_temp.chargeCurrency = b.name
and ( to_date(sale_upgrades_temp.workCompleted)
>= b.effectivePeriodStartDate)
and (to_date(sale_upgrades_temp.workCompleted))
<= b.effectivePeriodEndDate
OR b.effectivePeriodEndDate is null))
where sale_upgrades_temp.chargeCurrency
in (select name from CurrencyConversion);