帮我看看这个Sql server语句如何转成Oracle语句！

[pengjiangping]

if not Exists(select * from Counter where KeyValue=vcKeyValue) then
insert into Counter(KeyValue) Values(vcKeyValue)
else
select isnull(CountValue,0) into iCountValue from Counter where
KeyValue=vcKeyValue;
end if;
关键是不知道Exists和isNull在oracle中对应的函数是什么，
　　另外想问一下，在oracle中如何查到这些函数的帮助
　　我用的是oracle8.05

[bzszp]

select count(1) into t_num from Counter where KeyValue=vcKeyValue;
if t_num =0 then
....
else
select nvl(CountValue,0) into ...
end if;

[wanghai]

isNull--nvl

[pengjiangping]

谢谢两位的指教