How to format results in Postgres? - sql

Question

I need to show the location of content within a course that lives in a Virtual Learning Environment (VLE) - basically it is a teaching and learning website that is backed by a Postgres database.
I created the following query that returns the raw data. A sample of this is below
WITH RECURSIVE folders AS(
SELECT ccs.pk1, ccs.parent_pk1, ccs.position, ccs.folder_ind, ccs.title
FROM course_contents ccs
INNER JOIN course_main cm ON cm.pk1 = ccs.crsmain_pk1
WHERE cm.course_id = '<COURSE ID>'
and ccs.pk1 = '<INDEX>' -- primary key
UNION ALL
SELECT cc.pk1, cc.parent_pk1, cc.position, cc.folder_ind, cc.title
FROM course_contents cc
JOIN folders ON folders.pk1 = cc.parent_pk1
)
SELECT f.*
FROM folders f
SAMPLE DATA
PK1
PARENT_PK1
POSITION
FOLDER
TITLE
11497702
NULL
0
Y
Assessment
11497708
11497702
0
N
Using the Assessment Tools
11497709
11497702
1
N
Past Exams Papers
11497710
11497702
2
N
Using the Assessment Tools
11497711
11497702
3
N
Past Exams Papers
I would like to display it like the table below. Something to note is that there are multiple levels - files in folders, and folders in folders, etc.
PATH
Assessment - Using the Assessment Tools
Assessment - Past Exams Papers
Assessment - Using the Assessment Tools
Assessment - Past Exams Papers
I've used the following line
SELECT STRING_AGG(f.title,' - ') AS path
FROM folders f
GROUP BY f.parent_pk1
but it displays like
PATH
Assessment
Using the Assessment Tools - Past Exams Papers - Using the Assessment Tools - Past Exams Papers"
Any help would be very much appreciated.
Thanks

Answer 1

Hmmm . . . I think you want something like this rather than aggregation:
select f.*
from (select first_value(f.title) over (order by position) || '-' || first_value(f.title) over (order by position desc)
from folders f
) f
where folder = 'N';

Answer 2

Thanks to Gordon's answer above I have found the answer I was looking for.
I made a few changes to Gordon's code. Please see below. I do need to test this with more data though to see if it fully replicates the content structure.
select f.*
from (select first_value(f.title) over (order by position) || ' > ' ||
f.title
from folders f
where f.folder_ind = 'N'
) f