Urgent - general question - cursor related, maybe?

Question

Background:
I have a hierarchy of tables say A,B,C, each having a one to many relationship (A 1..n B 1..n C). I want to set one of the columns of A to a value of the primary key of one of the rows of B or C. The logic that I need to set the value in A is as follows:
If one of the rows in B has one of the several columns = NULL(start with the column on the left and keep going to the right) then I need to set the primary for that row in B to the column in A.
If all columns in all the rows in B <> NULL, then I need to drill down deeper into table C to do the same and set the Column in Table A to a value if I find a discrepnacy.
Question:
Is it possible to do this without using cursors? My boss thinks it can be done without using cursors. I don't see how it is possible. But if anyone has an idea please let me know.
Thanks in advance.

Answer 1

SQL> -- test data:
SQL> SELECT * FROM a
  2  /
     PK_ID COL       COL2 COL3 COL4 COL5                                                           
         1 ABC        123 FRED ?    *                                                              
         2 XYZ        789 MIKE ??   **                                                             
SQL> SELECT * FROM b
  2  /
     PK_ID       FK_A   COL1CODE   COL2CODE   COL3CODE COL1DESC COL2DESC COL3DESC                  
         5          1        111        222        333 ABC      SDF      TEST                      
         6          1        444        555        666 A35                                         
         7          2        111        222        333 ABC      SDF      TEST                      
         8          2        888        222        999 A60      B45                                
SQL> -- update:
SQL> UPDATE a
  2  SET    col4 =
  3           (SELECT pk_id
  4            FROM   (SELECT pk_id, fk_a,
  5                     NVL2 (col1desc,
  6                        NVL2 (col2desc,
  7                           NVL2 (col3desc, NULL, col3code),
  8                           col2code),
  9                        col1code) AS colcode,
10                     ROW_NUMBER () OVER (PARTITION BY fk_a ORDER BY pk_id) AS rn
11                 FROM   b
12                 WHERE  NVL2 (col1desc,
13                        NVL2 (col2desc,
14                           NVL2 (col3desc, NULL, col3code),
15                                 col2code),
16                           col1code) IS NOT NULL)
17            WHERE  rn = 1
18            AND    fk_a = a.pk_id),
19           col5 =
20           (SELECT colcode
21            FROM   (SELECT pk_id, fk_a,
22                     NVL2 (col1desc,
23                        NVL2 (col2desc,
24                           NVL2 (col3desc, NULL, col3code),
25                           col2code),
26                        col1code) AS colcode,
27                     ROW_NUMBER () OVER (PARTITION BY fk_a ORDER BY pk_id) AS rn
28                 FROM   b
29                 WHERE  NVL2 (col1desc,
30                        NVL2 (col2desc,
31                           NVL2 (col3desc, NULL, col3code),
32                                 col2code),
33                           col1code) IS NOT NULL)
34            WHERE  rn = 1
35            AND    fk_a = a.pk_id)
36  WHERE EXISTS
37           (SELECT pk_id
38            FROM   (SELECT pk_id, fk_a,
39                     NVL2 (col1desc,
40                        NVL2 (col2desc,
41                           NVL2 (col3desc, NULL, col3code),
42                           col2code),
43                        col1code) AS colcode,
44                     ROW_NUMBER () OVER (PARTITION BY fk_a ORDER BY pk_id) AS rn
45                 FROM   b
46                 WHERE  NVL2 (col1desc,
47                        NVL2 (col2desc,
48                           NVL2 (col3desc, NULL, col3code),
49                                 col2code),
50                           col1code) IS NOT NULL)
51            WHERE  rn = 1
52            AND    fk_a = a.pk_id)
53 
SQL> /
2 rows updated.
SQL> -- results:
SQL> SELECT * FROM a
  2  /
     PK_ID COL       COL2 COL3 COL4 COL5                                                           
         1 ABC        123 FRED 6    555                                                            
         2 XYZ        789 MIKE 8    999