Handling iteration in SQL

Question

Hi
I have a requirement where, given a contract (site) and part number I need to find the preferred supplier.
I had asked previously on this forum and thought I had be3en given a working solution with connect by prior and use of nocycle.
However, my data example was not good enough to test all scenarios, or at least enough scenarios.
I have a supplier table, which has a vendor number and an acquisition site.
I also have a purchase part supplier table which has for a given contract and part number, vendor number and whether the supplier is a primary vendor for that contract/part number.
In essence, for a given contract and part number I need to return the preferred vendor number.
However, there may be a few iterations to get that, because where the acquisition site for a supplier is not blank, I need to then use this as a link for to get the next supplier.
As usual, example helps, I think.
Consider this data:
Supplier:
Vendor_no  Acquisition_site
1000       UK1
1001       UK3
1002       UK1
1003       blank
1004       UK2
1005       UK1
1006       UK2
1007       blank
1008       blank
Purchase_Part_Supplier:
Contract Part_no Vendor_no Primary_Vendor_db
UK1      A       1000      N
UK1      A       1001      N
UK1      A       1002      Y
UK2      A       1001      Y
UK3      A       1000      N
UK4      A       1006      Y
UK1      B       1004      Y
UK2      B       1001      Y
UK3      B       1007      Y
UK4      B       1008      YThis can be created as:
with
supplier as (
select 1000 vendor_no, 'UK1' acquisition_site from dual UNION ALL
select 1001, 'UK3' from dual UNION ALL
select 1002, 'UK1' from dual UNION ALL
select 1003, null from dual UNION ALL
select 1004, 'UK2' from dual UNION ALL
select 1005, 'UK1' from dual UNION ALL
select 1006, 'UK2' from dual UNION ALL
select 1007, null from dual UNION ALL
select 1008, null from dual
purchase_part_supplier as (
select 'UK1' contract, 'A' part_no, 'N' primary_vendor_db, 1000 vendor_no from dual UNION ALL
select 'UK1', 'A', 'N', 1001 from dual UNION ALL
select 'UK1', 'A', 'Y', 1002 from dual UNION ALL
select 'UK2', 'A', 'Y', 1001 from dual UNION ALL
select 'UK3', 'A', 'N', 1000 from dual UNION ALL
select 'UK4', 'A', 'Y', 1006 from dual UNION ALL
select 'UK1', 'B', 'Y', 1004 from dual UNION ALL
select 'UK2', 'B', 'Y', 1001 from dual UNION ALL
select 'UK3', 'B', 'Y', 1007 from dual UNION ALL
select 'UK4', 'B', 'Y', 1008 from dual
)I create a single list by joining the data as follows:
select s.vendor_no, s.acquisition_site, pps.contract, pps.part_no
from  supplier s, purchase_part_supplier pps
where s.vendor_no=pps.vendor_no(+) and primary_vendor_db(+)='Y'This generates a list like this (I believe!):
vendor_no  acquisition_site  contract  part_no
1000       UK1              
1001       UK3               UK2       A
1001       UK3               UK2       B
1002       UK1               UK1       A
1003       blank            
1004       UK2               UK1       B
1005       UK1              
1006       UK2               UK4       A
1007       blank             UK3       B
1008       blank             UK4       BWhere I need to find the preferred vendor number for contract UK4, part number B the acquisition site for UK4/B is blank, so the vendor number is 1008 (the last row is the data set)
For contract UK2, part number B, the acquisition site (for contract UK2, part number B) is UK3 so we try again with this combination.
The acquisition site (for contract UK3, part number B) is blank and the vendor number is 1007 so this is returned.
However, to cater for bad data, consider where we look for contract UK1 and part number A. The acquisition site is UK1 which is the same as the contract, so this would create an infinite loop. Therefore we need to abort as such.
Also, consider contract UK3, part number A. There is no row at all for this, so again, abort accordingly.
The following scenarios are, to my knowledge the required results.
Starting    Result
Cont  Part 
UK1   A     Returns vendor_no 1002, acquisition_site UK1.  Since the acquisition_site = contract this is infinite cycle, so abort as 'infinite cycle'.
UK2   A     Returns vendor_no 1001, acquisition_site UK3.
UK3   A     No row found, abort as 'no primary supplier found'.
UK3   A     No row found, abort as 'no primary supplier found'.
UK4   A     Returns vendor_no 1006, acquisition_site UK2. 
UK2   A     Returns vendor_no 1001, acquisition_site UK3.
UK3   A     No row found, abort as 'no primary supplier found'.
UK1   B     Returns vendor_no 1004, acquisition_site UK2.
UK2   B     Returns vendor_no 1001, acquisition_site UK3.
UK3   B     Returns vendor_no 1007, acquisition_site blank.  Return 1007 as vendor number.
UK2   B     Returns vendor_no 1001, acquisition_site UK3.
UK3   B     Returns vendor_no 1007, acquisition_site blank.  Return 1007 as vendor number.
UK3   B     Returns vendor_no 1007, acquisition_site blank.  Return 1007 as vendor number.
UK4   B     Returns vendor_no 1008, acquisition_site blank.  Return 1008 as vendor number.Can this be done or will I have to resort to PL/SQL?
Thanks
Martin

Answer 1

Well, I believe I have cracked it!
with
supplier as (
select 1000 vendor_no, 'UK1' acquisition_site from dual UNION ALL
select 1001, 'UK3' from dual UNION ALL
select 1002, 'UK1' from dual UNION ALL
select 1003, null from dual UNION ALL
select 1004, 'UK2' from dual UNION ALL
select 1005, 'UK1' from dual UNION ALL
select 1006, 'UK2' from dual UNION ALL
select 1007, null from dual UNION ALL
select 1008, null from dual
purchase_part_supplier as (
select 'UK1' contract, 'A' part_no, 'N' primary_vendor_db, 1000 vendor_no from dual UNION ALL
select 'UK1', 'A', 'N', 1001 from dual UNION ALL
select 'UK1', 'A', 'Y', 1002 from dual UNION ALL
select 'UK2', 'A', 'Y', 1001 from dual UNION ALL
select 'UK3', 'A', 'N', 1000 from dual UNION ALL
select 'UK4', 'A', 'Y', 1006 from dual UNION ALL
select 'UK1', 'B', 'Y', 1004 from dual UNION ALL
select 'UK2', 'B', 'Y', 1001 from dual UNION ALL
select 'UK3', 'B', 'Y', 1007 from dual UNION ALL
select 'UK4', 'B', 'Y', 1008 from dual
select nvl(return_value,default_value) return_value from
select 1 lnk, decode(CONNECT_BY_ISCYCLE,1,'**DataCyc', decode(acquisition_site, null, to_char(vendor_no,999999), '**DataMiss')) return_value
from
select s.vendor_no, s.acquisition_site, pps.contract, pps.part_no
from  supplier s, purchase_part_supplier pps
where s.vendor_no=pps.vendor_no(+) and primary_vendor_db(+)='Y'
) q
where CONNECT_BY_ISCYCLE=1 or CONNECT_BY_ISLEAF=1
start with contract='UK3' and part_no='A'
connect by nocycle
prior acquisition_site=contract and prior part_no=part_no
(select 1 dftlnk, '**DataMiss' default_value from dual)
where dftlnk=lnk(+)