如何限制 Listagg 结果

Question

I have a table with lots of employment info and I used listagg to list all employments for each user, each user on a row instead of the max decode route. Using listagg works but I want to restrict it to just the first 5 for example. Some staff have over 30 employments listed.

select distinct emp.id_Staff,
  count (*) as cnt,
  LISTAGG (emp.employer_name || '('|| emp.job_title || ')', ', ')
    WITHIN GROUP (ORDER BY emp.employer_name) AS Employ_info
from (
  SELECT distinct em.id_Staff, em.employer_name,
    em.job_title, em_job_status
  FROM employment em
  where em.job_status = 'Active'
) emp
group by emp.id_Staff

Answer 1

You can use row_number() to enumerate the values. Then use a case in listagg() to just take the first five records:

select e.id_Staff,
       count(*) as cnt,
       listagg(case when seqnum <= 5 then e.employer_name || '('|| e.job_title || ')' end, ', ')
           within group (order by e.employer_name) AS Employ_info
from (select e.*,
             row_number() over (partition by e.id_staff order by e.id_staff) as seqnum
      from (select distinct em.id_Staff, em.employer_name, em.job_title, em_job_status
            from employment em
            where em.job_status = 'Active'
           ) e
     ) e
group by e.id_Staff