Max of a part of split string - sql

Question

I have, in my DB oracle 10g, a field that contains references.
It's stored as : name/yyyy/mm/number
The new number, is the max number found in the part mm/number.
So, for now, I have a split of my string that gives me a list of str_array like this :
str_array(name, yyyy, mm, number)
I'd like, with this, found max number, for the couple mm/number.
Is this possible to do this?
Can I have something like :
SELECT MAX(split(reference, '/').lastPartOfArray) into nb
FROM table
where lastPartOfArray-1 = sysdate.month;
Data samples :
Smith/2013/12/1
Smith/2013/11/1
Smith/2013/12/3
Jones/2013/12/6
Smith/2013/12/3
Jones/2013/11/7
Since we are in the month 12, a max on those data must give me 6 into nb.
The number part, has no limit, it can be 1000, 10000...
The part Jones/2013 doesn't really matter for the number. But I can't have the same number, for a month.
My apologies, I don't know if this is possible, so I tried to write what I want in the query.
Is this possible, or should I create more than one field in my table(name/yyyy, mm, number)?
edit : valex answer and some custom
select MAX(CAST(SUBSTR(num,INSTR(num,'/')+9,1000) as Int))
from T
where num like TO_CHAR(sysdate,'%/YYYY/MM/%')
So this, count searching first occurence.
select MAX(CAST(SUBSTR(num,INSTR(num,'/',1 ,n)+1,1000) as Int))
from T
where num like TO_CHAR(sysdate,'%/YYYY/MM/%')
This found the n occurence of the char.
This is a helpful solution in other cases.

Answer 1

To get a maximum you should convert this last part into INT values otherwise you can get not right results because of STRING comparing rules will be used.
As soon as /YYYY/MM/ has got a fixed length = 9 so we can find first \ position and add 9 to this position to find a last part number substring start.
Here is an example:
select MAX(CAST(SUBSTR(num,INSTR(num,'/')+9,1000) as Int))
from T
where num like TO_CHAR(sysdate,'%/YYYY/MM/%')
SQLFiddle demo
Also you can exclude wrong formatted values from this query to avoid conversion errors using the following way:
select MAX(CAST(SUBSTR(num,INSTR(num,'/')+9,1000) as Int))
from T
where num like TO_CHAR(sysdate,'%/YYYY/MM/%')
AND
LENGTH(TRIM(TRANSLATE(SUBSTR(num,INSTR(num,'/')+9,1000),
' 0123456789', ' '))) is null
SQLfiddle demo

Answer 2

Try this:
SELECT
MAX(SUBSTR(num, INSTR(num, '/', 1, 3) + 1))
FROM ref
WHERE
SUBSTR(num, INSTR(num, '/', 1, 2) + 1, INSTR(num, '/', 1, 3) - INSTR(num, '/', 1, 2) - 1) = TO_CHAR(sysdate, 'MM')
Sample: http://sqlfiddle.com/#!4/1b03a/1