SELECT email_address, rownum
FROM employee

EMAIL_ADDRESS             ROWNUM
--------------------- ----------
dpeguero                       1
kjohanse                       2
hbonnely                       3
hboye                          4
hballerm                       5
cbinow                         6
fmarkuss                       7
tlindens                       8
vrasmuss                       9
snederg                       10

Now I ran this query again with an order by clause :
SELECT email_address, rownum
FROM employee
ORDER BY email_address
EMAIL_ADDRESS      ROWNUM
--------------     ---------
2arthurs                   1
5pelava                    2
a_nguyen                   3
aaaceves                   4
aaad                       5
aaallen                    6
aaallred                   7
aabarca                    8
aabbas                     9
aabbott                   10