SQL query issue, how to improve it?

Question

Hello all, I want to create a query with with result in the following result. Every first person of an department starts with the letter A and goes up like this:
Name department
A Person1 3
B Person2 3
C Person3 3
D Person4 3
E Person10 3
A Person6 10
B Person7 10
C Person8 10
A Person4 13
B Person9 13
It has to be a SQL query, unfortunately no PL/SQL
I was able to create this query, but its lacking. Department_id will be a variable, a person can choose one department or several departments, so the query varies in size.
select chr(64+rownum), name, department_id
from ( select name, department_id
from employees
where department_id = 3
order by id_but, naam
union
select chr(64+rownum), name, department_id
from ( select name, department_id
from employees
where department_id = 10
order by id_but, naam
union
select chr(64+rownum), name, department_id
from ( select name, department_id
from employees
where department_id = 13
order by id_but, naam
order by id_but, naam
The employees table has the following columns:
id, name, department_id
Can anyone help me make this query better? parhaps with the With clause?

Answer 1

Use analytic function ROW_NUMBER:
with t as (
           select 'A' name,3 department from dual union all
           select 'B',3 from dual union all
           select 'C',3 from dual union all
           select 'D',3 from dual union all
           select 'E',3 from dual union all
           select 'A',10 from dual union all
           select 'B',10 from dual union all
           select 'C',10 from dual union all
           select 'A',13 from dual union all
           select 'B',13 from dual
select  name,
        'Person' || row_number() over(partition by department order by name) person,
        department
  from  t
  order by 3,
           3
NAME                           PERSON                                         DEPARTMENT
A                              Person1                                                 3
B                              Person2                                                 3
C                              Person3                                                 3
D                              Person4                                                 3
E                              Person5                                                 3
A                              Person1                                                10
B                              Person2                                                10
C                              Person3                                                10
A                              Person1                                                13
B                              Person2                                                13
10 rows selected.
SQL> SY.