Oracle move strings to another matching row

I have a table called tblrespondent and my data looks like this:

orclid13 | casenm    | commentfld
-------------------------------
27527     2021JV0039  grandmother
27528     2021JV0039  of Liliana/ Possibly Deceased
27529     2021JV0039  Possibly deceased.
27530     2021JV0039  whereabout unknown.
27531     2021JV0039

I have several case numbers that have multiple rows like this and I need to move all the comments into the lowest orclid13. The result would look like this with a semicolon in between each comment.

orclid13 | casenm    | commentfld
-------------------------------
27527     2021JV0039  grandmother; of Liliana/ Possibly Deceased; Possibly deceased.; whereabout unknown.
27528     2021JV0039  
27529     2021JV0039  
27530     2021JV0039  
27531     2021JV0039

How would I approach this? Many thanks in advance!

Answer

Assuming you need a select query, this could be a way:

select orclid13, casenm,
        case
            when row_number()
                    over (partition by casenm order by orclid13) = 1
                then listagg (commentfld, ';')
                        within group (order by orclid13)
                        over (partition by casenm )
        end as commentfld
from tblrespondent

Basically, listagg aggregates all the comments into a single string, row_number() is used to determine whether you are on the first row of the casenm set and this result is used by the case to show the concatenated string only in the first row of the set.

If you need to update your table, you can use the same logic above in a merge:

merge into tblrespondent t
using (
        select orclid13, casenm, rowid,
                case
                    when row_number()
                            over (partition by casenm order by orclid13) = 1
                        then listagg (commentfld, ';')
                                within group (order by orclid13)
                                over (partition by casenm )
                end as new_commentfld
        from tblrespondent
       ) X
on (x.rowid = t.rowid)
when matched then update set t.commentfld = X.new_commentfld