Build a three table join with a recusive table in the middle?

I have three relevant tables: Parts, PartGroup, and MarkupGroup.

Parts is simple.

PartID          artificial primary key
Part            part number
PartGroupID     Foreign key

sample data:

1   T1000           5
2   wizbang gold    17
3   flux capacitor  2

PartGroup is an Acyclic Directed Graph(tree) modeled with a self-linked parent key

PartGroupID     artificial primary key
Description     name of group
ParentID        foreign key linked to PartGroupID
MarkupGroupID   foreign key linked to MarkupGroup

Sample data would look like this-

1   system      null    null
2   component   null    1 
3   software    null    2
4   abc         1       3
5   xyz         1       4
6   123         4       null
7   456         4       null
8   789         5       null
9   a1          6       null
10  b2          6       null
11  c3          7       null
12  d4          7       null
13  e5          8       null  
14  f6          8       null
15  alpha       3       null
16  beta        3       null
17  gamma       3       null

MarkupGroup is to apply a markup factor to several PartGroups as a set.

MarkupGroupID   primary key
MarkupFactor    numeric attribute field

sample data-

1   15
2   20
3   25
4   22

I need to write a query that returns the appropriate markup amount for each part in the parts table. There is never a case when more then one markup can apply to a part. I need to recurse up the graph to find the markup, and I won't know at query time how many levels I need to recurse to find a non-null markup.

There is never a case when a part will encounter more than one possible join to a margin on the way up the tree, so there's no accumulation that needs to be done.

The t1000 is of type xyz, which has a foreign key to a MarginGroup, so we can join and get a value. It also has a parent, but that's irrelevant since we have the value we need.

Wizbang Gold is gamma-group software, which has no foreign key, but the pa

You can do the recursion in a CTE from the top down carrying MarkupGroupID with you.

with C as
(
  select P.PartGroupID,
         P.ParentID,
         P.MarkupGroupID
  from PartGroup as P
  where P.ParentID is null
  union all 
  select P.PartGroupID,
         P.ParentID,
         coalesce(P.MarkupGroupID, C.MarkupGroupID)
  from PartGroup as P 
    inner join C 
      on P.ParentID = C.PartGroupID
)
select P.PartID,
       P.Part,
       MG.MarkupFactor
from Parts as P
  inner join C
    on P.PartGroupID = C.PartGroupID
  inner join MarkupGroup as MG
    on C.MarkupGroupID = MG.MarkupGroupID
order by P.PartID

SQL Fiddle

The recursive CTE will create a derived table that looks like this.

PartGroupID ParentID    MarkupGroupID
----------- ----------- -------------
1           NULL        NULL
2           NULL        1
3           NULL        2
15          3           2
16          3           2
17          3           2
4           1           3
5           1           4
8           5           4
13          8           4
14          8           4
6           4           3
7           4           3
11          7           3
12          7           3
9           6           3
10          6           3

If you need parts with partgroup not connected to a markup you can use a outer join against MarkupGroup in your main query.

with C as
(
  select ...
)
select P.PartID,
       P.Part,
       MG.MarkupFactor
from Parts as P
  inner join C
    on P.PartGroupID = C.PartGroupID
  left outer join MarkupGroup as MG
    on C.MarkupGroupID = MG.MarkupGroupID
order by P.PartID

StackExchange Database Administrators Q#22704, answer score: 5