SQL Max and Left functions

Question

In a table I have a field "Ticket No.". I am using Ticket No in a format like:
00021-10-06-0201
The first set (left side) represents Ticket No. Then month, year, and code.
Each time when a user wants to enter new record a new ID is generated as:
"Select max(Left(TicketID,5)) from Ticket".
The new id becomes result+1.
I want to know that the above field is a string. But when I use LEFT
function, as above, it successfully returns max of the first set. Does
it automatically converts it to Long integer?
If not, how to use it securely so that first the left set is converted
to Long Integer and then the MAX is found. All in SQL query.

Answer 1

I want to know whether your "substr(00021...)
approach and in my example, does max function
automatically converts it to a numeric type.I did not use MAX in my example, but still it is converting to numeric depending on the operator you are using. Elaborating....see below..
SQL> select substr('00021-10-06-0021',1,5)+1 from dual;
SUBSTR('00021-10-06-0021',1,5)+1
                              22
SQL> select substr('A0021-10-06-0021',1,5)+1 from dual;
select substr('A0021-10-06-0021',1,5)+1 from dual
ERROR at line 1:
ORA-01722: invalid number
SQL> select substr('A0021-10-06-0021',1,5)||'A' from dual;
SUBSTR
A0021ASee the above 1st and 3rd query, the behaviour is completely based on the operators.