sql server - sql statement to retrieve the last entry value from database -

my auto number has 2 parts

3 digits serial number , last 8 digits month , year of invoice

for example: 001072013

so if want next invoiceno

i select last entry of invoice number database

select top 1 invoiceno  buyinvoice 

cut first 3 digits, , make increment, , combine month , year of invoice

so 002072013

the problem above statement doesn't return last entry value

and ascending , descending both don't work

i try:

select top 1 invoiceno  buyinvoice order right(invoiceno,4) desc,   right(invoiceno, 6) desc,    invoiceno desc