Question

I have records with a project id and an ‘inherit id’, i.e. the project that the current project inherits from. The inheritance level is unknown.

I now need to collapse this to: ‘inherit from the top most’

E.g.:

1006 <- 1005 <- 1002 <- 999

prj_id / inherit_id

999  / 1002

1002 / 1005

1005 / 1006

should collapse to

1006 <- 1005 

1006 <- 1002

1006 <- 999

prj_id / inherit_id

999  / 1006

1002 / 1006

1005 / 1006

Can this be done in SQL statement without loops?
Creating temporary tables is fine.
It should work for FireBird, SQL Server, Oracle 9+ (i.e. 3 sets of statements is fine)

I only got this far:

Records that inherit from a record that itself inherits again:

select tt_prj_id,tt_name,tt_inherit_id from tt_prj a

where a.tt_inherit_id in

(select tt_prj_id from tt_prj b

 where b.tt_inherit_id is not null

 and b.tt_inherit_id > 0)

Who can help me further?

Answer 1

Something like the following should get you started (it’s not the final solution!):

with recursive project_tree as (
   select tt_prj_id, cast(tt_prj_id as varchar(500))||'/' as id_path, tt_prj_id as root_id
   from tt_prj
   where tt_inherit_id = 0

   union all

   select c.tt_prj_id, id_path || cast(c.tt_prj_id as varchar(100)) ||'/', null
   from tt_prj c
     join project_tree p on c.tt_inherit_id = p.tt_prj_id
)
select *
from project_tree;

This works Firebird 2.5 (might also work with 2.1, but I don’t have one at hand right now)

It should work with SQL Server when you remove the keyword recursive (which is required by the ANSI standard, but since when did Microsoft care about that…) and you need to replace the standard string concatention || with the + operator.

Oracle does only support recursive CTEs before 11.2.
In prior version you need to rewrite this using CONNECT BY, which woudl be something like this:

select tt_prj_id, tt_inherit_id, sys_connect_by_path(tt_prj_id, '/')
from tt_prj
start with tt_inherit_id = 0
connect by prior tt_prj_id = tt_inherit_id;