DB2 : search depth first : (syntax) error - sql

Question

A few days ago I installed DB2 LUW (11.5) on a server to play around with.
Now I would like to do some recursive SQL (Recursive Common Table Expression):
Let me show how I setup :
drop table relations;
create table relations (id int, parent int);
insert into relations values(0,NULL);
insert into relations values(1,0);
insert into relations values(2,1);
insert into relations values(3,1);
insert into relations values(4,3);
insert into relations values(5,0);
insert into relations values(6,5);
insert into relations values(7,5);
insert into relations values(8,6);
insert into relations values(9,7);
insert into relations values(10,0);
insert into relations values(11,1);
commit;
Now I would like to see the hierarchy in the table. So I tried the following:
with recur(id, parent, level) as
(
select rel.id id, rel.parent parent, 0 level from relations rel where rel.id=0
union all
select rel.id, rel.parent, rec.level+1 from recur rec, relations rel where rec.id=rel.parent
and rec.level<10
)
select id, lpad(parent, level*2, ' ') from recur;
This gives me:
ID PARENT
----------- ------------------
0 -
1 0
5 0
10 0
2 1
3 1
11 1
6 5
7 5
4 3
8 6
9 7
This is (to me) : "Search Breadth First"
What I would like to see is "Search Depth First"
So I did this:
with recur(id, parent, level) as
(
select rel.id id, rel.parent parent, 0 level from relations rel where rel.id=0
union all
select rel.id, rel.parent, rec.level+1 from recur rec, relations rel where rec.id=rel.parent
and rec.level<10
)
search depth first by parent set ord
select id, lpad(parent, level*2, ' ') parent from recur order by ord;
But this delivers to me:
SQL0104N An unexpected token "search depth first by parent set ord sel" was
found following "t and rec.level<10 )". Expected tokens may include:
"<values>". SQLSTATE=42601
No clue how to solve it now. I (think I) have tried a lot of possible solutions. But none worked.
I'm starting to believe that DB2 LUW (11.5) doesn't know about Search Depth First. Or some setting must be made to make DB2 aware of the "SDF" possibility.
My question to you all:
How to solve this problem? How do I get Search Depth First to work?
On the positive....following works like a charms....but that is not whatI want tot know :-)
select id, lpad(parent, level*2, ' ') parent, level
from relations
start with id=0
connect by prior id=parent;
ID PARENT LEVEL
----------- ---------- -----------
0 - 1
1 0 2
2 1 3
3 1 3
4 3 4
11 1 3
5 0 2
6 5 3
8 6 4
7 5 3
9 7 4
10 0 2
This works like a charm, but I had tot make a switch in the database (and a restart):
db2set DB2_COMPATIBILITY_VECTOR=08

Answer 1

Your question is about displaying rows in a specific ordering, not about searching in a specific ordering.
You can display the rows in the ordering you want by assembling an ordering column that fits your needs.
For example:
with
n (id, parent, lvl, ordering) as (
select id, parent, 1, lpad(id, 3, '0') || lpad('', 30, ' ')
from relations
where parent is null
union all
select r.id, r.parent, n.lvl + 1, trim(n.ordering) || '/' || lpad(r.id, 3, '0')
from n, relations r where r.parent = n.id
)
select id, lpad(parent, lvl * 2, ' ') as parent, lvl
from n
order by ordering;
Result:
ID PARENT LVL
--- --------- ---
0 1
1 0 2
2 1 3
3 1 3
4 3 4
11 1 3
5 0 2
6 5 3
8 6 4
7 5 3
9 7 4
10 0 2
See running example at db<>fiddle.