Query minimum quantity

Question

Good Morning Guru,
I have 2 tables, master inventory and master bill of material,
master bill of material is a produce structure that raw materials(RM) were needed to make a finish product (FG)
create table inven
( stock_num varchar2(10),
category varchar2(1),
QTY_OH number(10)
create table bom_d
( FG varchar2(10),
RM varchar2(10)
insert into inven values('A','F',0);
insert into inven values('B','F',0);
insert into inven values('A1','R',10);
insert into inven values('A2','R',7);
insert into inven values('A3','R',12);
insert into inven values('B1','R',10);
insert into inven values('B2','R',10);
insert into inven values('B3','R',5);
insert into bom_d values('A', 'A1');
insert into bom_d values('A', 'A2');
insert into bom_d values('A', 'A3');
insert into bom_d values('B', 'B1');
insert into bom_d values('B', 'B2');
insert into bom_d values('B', 'B3');
commit;
select * from inven;
SQL> select * from inven;
STOCK_NUM C QTY_OH
A F 0
B F 0
A1 R 10
A2 R 7
A3 R 12
B1 R 10
B2 R 10
B3 R 5
SQL> select * from bom_d;
FG RM
A A1
A A2
A A3
B B1
B B2
B B3
SQL> select fg,rm,stock_num, qty_oh
2 from inven i, bom_d b
3 where rm=stock_num
4 /
FG RM STOCK_NUM QTY_OH
A A1 A1 10
A A2 A2 7
A A3 A3 12
B B1 B1 10
B B2 B2 10
B B3 B3 5
I want to display :
only one for each FG that has minium qty_oh
(I want to display as bellow)
FG RM STOCK_NUM QTY_OH
A A2 A2 7
B B3 B3 5
need help, how to make the sql?
using oracle 8i
Thank you very much

Answer 1

Hi,
That's called a Top-N Query .
Here's one way to do it:
SELECT     fg
,     rm
,     stock_num
,     qty_oh
FROM     (     -- Begin in-line view to compute r_num
          SELECT     b.fg
          ,     b.rm
          ,     i.stock_num
          ,     i.qty_oh
          ,     RANK () OVER ( PARTITION BY  b.fg
                                  ORDER BY          i.qty_oh
                              ) AS r_num
          FROM     bom_d     b
          ,     inven     i
          WHERE     b.rm     = i.stock_num
     )     -- End  in-line view to compute r_num
WHERE     r_num     = 1
;What do you want to do if there happens to be a tie for the lowest qty_oh (for example, if you change the qty_oh to 10 for stock_num='B3')? The query above will include all the items with the lowest qty_oh (that is, all 3 rows with fg='B' and qty_oh=10).