Question

I have a single table that lists dependencies and I can’t figure out how I can sort this in the actual order the diagram is displayed (using DB2 SQL)

Diagram (Lists out the GROUP)
34 -> 23 -> 65 ->….

The goal is to sort in the order of the diagram

The Table has two fields GROUP and DEPEND. The ideal first column would be 34,0 (0 since it is dependent on nothing) followed by 23,34 (dependent on GROUP 34), followed by 65,23 (dependent on GROUP 23). Following the pattern of GROUP, DEPEND.

So the results would be as follows:

 1. GROUP   DEPEND
 2. 34      0
 3. 23      34
 4. 65      23

Is it possible to use a variable or something to view the previous record’s GROUP to determine the next row?

Thanks so much for any assistance or ideas

Answer 1

Current versions of DB2 support recursive queries, so the following should work (at least it does with my DB2 9.7 Express-C on Windows):

with dep_tree  (groupno, depend, group_order) as (
   select groupno, depend, 1 as group_order
   from group_list
   where depend = 0

   union all 

   select c.groupno, c.depend, p.group_order + 1
   from group_list c, 
        dep_tree p 
   where p.groupno = c.depend
)
select group_order, groupno, depend
from dep_tree
order by group_order;

Note that I used groupno instead of GROUP as the column name, because GROUP is a reserved word and should not be used as a column name.