"MacGregor, Ian A." wrote:
>
> Given the following Table
>
> emplid course_id
> ------ ---------
> 1 1
> 2 2
> 2 3
> 3 3
> 3 4
> 3 5
> 4 3
> 4 4
> 4 5
> 5 2
> 5 3
> 6 1
> 7 2
> 8 3
> 8 4
>
>--------------------------------------------------------------------------------------------
> What statement would you write to group employees by the set of courses they have
>taken. In otherwords each employee in a group must have taken the same as the
>others in the group, not one class more nor less. In this example the employees
>making up the groups would be
>
> 1,6
> 2,5
> 3,4
> 7
> and 8
>
> I had this posed by one of my developers. He had also come up with a solution
>which didn't take a relational approach. The approach is not exotic, and I suspect
>it will be proposed by many people. He'd like a relational one.
>
> Ian MacGregor
> Stanford Linear Accelerator Center
> [EMAIL PROTECTED]
I don't think you can, unless, perhaps, you use the analytical functions
which I have never had the opportunity to play with. Problem number 1
is getting an identifier for each set of courses. Since you must get
this through a 'GROUP BY', the only chance is a numerical expression. An
obvious candidate is something like sum(course_id * power(10, n -1))
where n is the order (starting with 1) of course ids suitably ordered
for each employee - restarting from 1 with each employee. Getting n is
the trouble. You cannot get it through rownums and in-line views, it
would require some kind of ugly three-way correlation between views in
the FROM clause and a subquery. The best solution I see, but it's not a
'pure play' one, is to create a function
create or replace function course_index(p_emplid in number,
p_course_id in number)
return number
as
n_val number;
begin
select a.n
into n_val
from (select b.course_id, rownum n
from (select course_id
from courses_taken
where emplid = p_emplid
order by 1 desc) b) a
where a.course_id = p_course_id;
return n
exception
when no_data_found then
return null;
end;
Then it becomes relatively easy to write
select emplid, sum(course_id * power(10, course_index(emplid,
course_id) - 1) course_set
from courses_taken
group by emplid
and then to do whatever you want.
--
Regards,
Stephane Faroult
Oriole Corporation
Voice: +44 (0) 7050-696-269
Fax: +44 (0) 7050-696-449
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Author: Stephane Faroult
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