SLOW Query ... Need help improving performance

Question

Database: Oracle 8i
Note: I don't have a whole lot of experience with writing queries, so please forgive me for any dumb mistakes I most likely made.
I have a query in which I have a SUM in two levels. I think this is probably the root cause of the very slow performance of the query. However, I just don't see any way around it, and can't come up with any other ways to speed up the query. The query itself only returns one line, the summary line. And, by slow, I mean it can take up to an hour or two. This is a query I need to run multiple times, based on some parameters that I cannot query from a database.
The query basically calculates the current unit cost of a part. It has to sum up the issue cost of the part (cost of material issued to the part's order), the actual dollars put into a part (labor, etc.), and the burden dollars associated with the part. This sum has to be divided by the total quantity of parts completed on the part's order to get the unit cost. I have to account for the possibility that the quantity complete is 0, so that I don't end up dividing by 0.
Below is my query, and sample data for it:
SELECT     a.part_nbr
,     a.mo_nbr
,     a.unit_iss_cost
,     CASE
          WHEN     a.qty_complete_ind     ='Nonzero'
          THEN     SUM(a.act_dlrs/a.qty_complete)
          ELSE     0
     END                                             AS unit_dlrs
,     CASE
          WHEN     a.qty_complete_ind     ='Zero'
          THEN     SUM(a.act_dlrs)
          ELSE     0
     END                                             AS qty_0_dlrs
FROM     (     SELECT     act.part_nbr                              AS part_nbr
          ,     act.order_nbr || '-' || act.sub_order_nbr          AS mo_nbr
          ,     ic.unit_iss_cost                         AS unit_iss_cost
          ,     SUM     (
                         act.act_dlrs_earned          +
                         act.act_brdn_dls_earned          +
                         act.tool_dlrs_earned          +
                         act.act_fix_brdn_dls_ea     
                    )                              AS act_dlrs
          ,     ord.qty_complete                         AS qty_complete
          ,     CASE
                    WHEN     ord.qty_complete     <>0
                    THEN     'Nonzero'
                    ELSE     'Zero'
               END                                   AS qty_complete_ind
          FROM     ACT          act
          ,     ISSUE_COST     ic
          ,     ORD          ord
          WHERE     ord.ord_nbr          =act.order_nbr          AND
               ord.sub_ord_nbr          =act.sub_order_nbr     AND
               ord.major_seq_nbr     =act.maj_seq_nbr     AND
               ic.ord_nbr          =act.order_nbr          AND
               ic.sub_ord_nbr          =act.sub_order_nbr     AND
                    (act.order_nbr          =LPAD(?,10,'0'))     AND
                    (act.sub_order_nbr     =LPAD(?,3,'0'))          AND
                    (act.activity_date     <=?)               
          GROUP BY     act.part_nbr
          ,          act.order_nbr || '-' || act.sub_order_nbr
          ,          act.maj_seq_nbr
          ,          ord.qty_complete
          ,          ic.unit_iss_cost
     ) a
GROUP BY     a.part_nbr
,          a.mo_nbr
,          a.unit_iss_cost
,          a.qty_complete_ind
CREATE TABLE ACT
          creation_date          date
     ,     c_id               number (5,0)
     ,     part_nbr          varchar(25)
     ,     order_nbr          varchar(10)
     ,     sub_order_nbr          varchar(3)
     ,     maj_seq_nbr          varchar(4)
     ,     act_dlrs_earned          number (15,2)
     ,     act_brdn_dls_earned     number (15,2)
     ,     tool_dlrs_earned     number (15,2)
     ,     act_fix_brdn_dls_ea     number (15,2)
     ,     activity_date          date
     CONSTRAINT     ACT_PK
     PRIMARY KEY     (creation_date, c_id)
);--Please note, issue_cost is actually a view, not a table, but by itself it runs very quickly
CREATE TABLE ISSUE_COST
          unit_iss_cost     number(15,2)
     ,     ord_nbr          varchar(10)
     ,     sub_ord_nbr     varchar(3)
);--Please note, ord table has a couple of foreign keys that I did not mention
CREATE TABLE ORD
          ord_nbr          varchar(10)
     ,     sub_ord_nbr     varchar(3)
     ,     major_seq_nbr     varchar(4)
     ,     qty_complete     number (13,4)
);Sample tables:
ACT
creation_date     c_id     part_nbr     order_nbr     sub_order_nbr     maj_seq_nbr     act_dlrs_earned     act_brdn_dls_earned     tool_dlrs_earned     act_fix_brdn_dls_ea     activity_date
01/02/2000      12345     ABC-123          0000012345     001          0010          10.00          20.00               0.00               0.00               01/01/2000
01/02/2000     12345     XYZ-987          0000054321     001          0030          100.00          175.00               10.00               10.00               01/01/2000
01/03/2000     12347     ABC-123          0000012345     001          0020          25.00          75.00               5.00               1.00               01/02/2000
01/03/2000     12348     ABC-123          0000012345     001          0020          75.00          120.00               25.00               5.00               01/02/2000
01/03/2000     12349     XYZ-987          0000054321     001          0050          50.00          110.00               0.00               0.00               01/02/2000
01/04/2000     12350     ABC-123          0000012345     001          0030          25.00          40.00               0.00               0.00               01/03/2000
ISSUE_COST
unit_iss_cost     ord_nbr          sub_ord_nbr
125.00          0000012345     001
650.00          0000054321     001
ORD
ord_nbr          sub_ord_nbr     major_seq_nbr     qty_complete
0000012345     001          0010          10
0000012345     001          0020          10
0000012345     001          0030          0
0000054321     001          0030          20
0000054321     001          0050          19If insert statements are needed for the sample tables, let me know and I'll go re-figure out how to write them. (I only have read-only access to the database I'm querying, so creating tables and inserting values aren't things I ever do).
Thanks in advance!

Answer 1

For diagnosing where the time of your query is being spent, we don't need create table and insert statements. If we execute your query with only a handful of rows, the query will be very fast. What we do need to know, is the plan the optimizer takes to compute your result set, and the cardinalities of each step.
Please read When your query takes too long ... carefully and post the full explain plan and tkprof output.
Regards,
Rob.