Calculating value based on parent/child relations for a column..

Question

Hi Friends,
I have a requirement thus,
sample table, parts,
ppart cpart qty
990 1234 200
100 100_1 150
100 100_2 2
100_1 120 100
100_1 121 200
100_2 130 50
where qty is a number and the rest are varchar fields. Here the ppart 100 is a parent value for cpart values 100_1 and 100_2. So, I need to multiply the qty value for a child with the parent's qty values. The final result would look like,
ppart cpart qty
990 1234 200
100 100_1 150
100 100_2 2
100_1 120 15000
100_1 121 30000
100_2 130 100
I have only a basic understanding of SQL but I couldnt figure out a way for this. My best try was to join the table with itself and equate the ppart and cpart columns to retrieve the qty. However, the actual table has about 50 million records and I guess my idea is not going to please my DBA! I would appreciate if you could suggest better ideas.
Thanks.

Answer 1

Hi,
you forgot nvl()
SQL> with parts as (select '990' ppart, '1234' cpart, 200 qty from dual union all
  2                select '100'  , '100_1', 150 from dual union all
  3                select '100'  , '100_2', 2   from dual union all
  4                select '100_1', '120'  , 100 from dual union all
  5                select '100_1', '121'  , 200 from dual union all
  6                select '100_2', '130'  , 50  from dual)
  7  select p.ppart parent_part, c.ppart child_part, p.qty parent_qty, p.qty * c.qty child_quantity
  8  from   parts c
  9  left join parts p on c.ppart = p.cpart
10  /
PAREN CHILD PARENT_QTY CHILD_QUANTITY                                          
100   100_1        150          30000                                          
100   100_1        150          15000                                          
100   100_2          2            100                                          
      990                                                                      
      100                                                                      
      100                                                                      
6 rows selected.
SQL> with parts as (select '990' ppart, '1234' cpart, 200 qty from dual union all
  2                select '100'  , '100_1', 150 from dual union all
  3                select '100'  , '100_2', 2   from dual union all
  4                select '100_1', '120'  , 100 from dual union all
  5                select '100_1', '121'  , 200 from dual union all
  6                select '100_2', '130'  , 50  from dual)
  7  select p.ppart,p.cpart, p.qty * nvl(c.qty,1) qty
  8  from   parts p,parts c
  9  where p.ppart = c.cpart(+)
10  /
PPART CPART        QTY                                                         
100_1 121        30000                                                         
100_1 120        15000                                                         
100_2 130          100                                                         
990   1234         200                                                         
100   100_2          2                                                         
100   100_1        150                                                         
6 rows selected.