Conversion of SQL Server UDF to Oracle

Question

Hi,
I hope this is the right place to post this question.
We are migrating a number of applications from SQL Server to Oracle, so my exposure/experience in Oracle is very limited.
I had previously created a functin in SQL Server which takes data in this format
Name, CC_Code
Alan, 3720
Alan, 3730
Alan, 3740
Anna, 5045
Barry, 5004
Barry, 7518
and produces this
Name, CC_Code
Alan, 3720, 3730, 3740
Anna, 5045
Barry, 5004, 7518
I was able to cobble together the select statement below, which returns the correct output, but I am unable to create it as a function.
SELECT name,
LTRIM(MAX(SYS_CONNECT_BY_PATH(cost_centre_code,', '))
KEEP (DENSE_RANK LAST ORDER BY curr),',') AS CC_Code
FROM (SELECT name,
cost_centre_code,
ROW_NUMBER() OVER (PARTITION BY name ORDER BY cost_centre_code) AS curr,
ROW_NUMBER() OVER (PARTITION BY name ORDER BY cost_centre_code) -1 AS prev
FROM (select * from mnt_staff, mnt_cost_centre_staff
where MNT_STAFF.employee_number = MNT_COST_CENTRE_STAFF.employee_number
and mnt_cost_centre_staff.association_flag = 'S'))
GROUP BY name
CONNECT BY prev = PRIOR curr AND name = PRIOR name
START WITH curr = 1;
When I create the function, using Toad for Oracle, I get no compile errors, but when I try and use it
select MNT_USER."NameSecondary"
FROM (select * from mnt_staff, mnt_cost_centre_staff
where MNT_STAFF.employee_number = MNT_COST_CENTRE_STAFF.employee_number
and mnt_cost_centre_staff.association_flag = 'S');
I get the following error
ORA-01422: exact fetch returns more than requested number of rows
ORA-06512: at "MNT_USER.NameSecondary", line 6
exact fetch returns more than requested number of rows
Cause: The number specified in exact fetch is less than the rows returned.
Action: Rewrite the query or change number of rows requested
I've looked at some suggestions
"to declare the select statement as a cursor, and a variable type ref cursor to
hold the results and return them to the caller (as an out parameter)" but am lost as to what/how to do this.
Any suggestions gratefully received.

Answer 1

What you posted as a SQL Server function is not a SQL Server function. Neither is your Oracle SQL statement a function. A function, in Oracle, takes one or more parameters (IN, OUT, or IN OUT) and returns one and only one value unless it is a pipelined table function.
To learn about Oracle functions
http://www.psoug.org/reference/functions.html
What is appears you have done is repeat a very common error which is to think that because you know a Microsoft product you can pick up an Oracle product, having not read the concepts and architecture docs, having not taken a class, and having not studied the subject, just start banging out code: It does not work that way.
Your SQL statement, NOT A FUNCTION, is this:
select MNT_USER."NameSecondary"
FROM (
  select *
  from mnt_staff, mnt_cost_centre_staff
  where MNT_STAFF.employee_number = MNT_COST_CENTRE_STAFF.employee_number
  and mnt_cost_centre_staff.association_flag = 'S');and none of us can fix it because none of us can do more than guess as to what is specifically wrong though at the same time I can easily state that it appears that a lot of it is wrong. What is the point of creating an in-line view when all you really seem to want is:
SELECT mnt_user NameSecondary
FROM mnt_staff ms, mnt_cost_centre_staff mc
WHERE ms.employee_number = mc.employee_number
AND mc.association_flag = 'S';