Rolling up multiple rows into a single row

Question

Need a query to get the name of the project and their respective employee first name who have a project assigned. If more than one employee is under a given project, then second column should have all the names separated by a comma. Example: Vikash, Ashish.

I have two tables:

Table1: EmployeeID, FirstName

1 Vikas
2 nikita
3 Ashish
4 Nikhil
5 anish

Table2: EmployeeDetailID, ProjectName
1|Task Track
1|CLP
1|Survey Managment
2|HR Managment
3|Task Track
3|GRS
3|DDS
4|HR Managment
6|GL Managment

I have used the following code to get employees name and project they are working on:

select  FirstName, ProjectName
from EmployeeInfo, EmployeeProjects
where EmployeeID = EmployeeDetailID;

OUTPUT:

Vikas Task Track
Vikas CLP
Vikas Survey Managment
nikita HR Managment
Ashish Task Track
Ashish GRS
Ashish DDS
Nikhil HR Managment

I don`t know how combine multiple rows and separate them using comma.

Answer 1

perhaps use a concatenation function that operates on a group like listagg :

select Table2.ProjectName, listagg(Table1.FirstName, ', ')
within group (order by Table1.FirstName) as members
from Table1, Table2
where Table1.EmployeeID = Table2.EmployeeDetailID
group by Table2.ProjectName

Answer 2

Try this:

SELECT
    T2.PROJECTNAME,
    RTRIM(XMLAGG(XMLELEMENT(E, T1.FIRSTNAME, ',').EXTRACT('//text()')
        ORDER BY
            T1.FIRSTNAME
    ).GETCLOBVAL(), ',') AS MEMBERS
FROM
    TABLE1 T1
    JOIN TABLE2 T2 ON ( T1.EMPLOYEEID = T2.EMPLOYEEDETAILID )
GROUP BY
    T2.PROJECTNAME;

LISTAGG will throw an error if your consolidated string becomes more than 4000 characters long.