Query to find 1:N relation from a table

Question

Hi,
I have a table where Material# & Item# are stored. Now Material# & Item# are related in 1:N.
e.g. (data)
MM# ITM# ..... <other attributes>
M1 I1 ..... <data for other attributes>
M1 I1 ..... <data for other attributes>
M1 I2 ..... <data for other attributes>
M2 I3 ..... <data for other attributes>
M3 I4 ..... <data for other attributes>
M3 I5 ..... <data for other attributes>
Now by somehow writing a single select query can I get the only one-2-many data. So that a person who is not aware of this relationship, will be easily able to identify.
e.g.
M1 I1
M1 I2
M3 I4
M3 I5
I am able to write the following query (please ignore the qualify keyword. I have used it because I have written this in teradata).
select subqry.itm_cd,subqry.mm_key
from
select mm_key,itm_cd,row_number() over (partition by mm_key,itm_cd order by mm_key) rn
from <my_table>
qualify rn = 1
) subqry
qualify row_number() over (partition by subqry.itm_cd order by subqry.itm_cd) > 1
order by subqry.itm_cd
This gives the output like :
M1 I2
M3 I4
But I want all the two occurrences of M1 and M3.
Regards,
Koushik Chandra

Answer 1

Very simple... group by mm#,itm#
SQL> create table test(mm# varchar2(3),itm# varchar2(2));
Table created.
SQL> insert into test values ('M1','I1');
1 row created.
SQL> insert into test values ('M1','I1');
1 row created.
SQL> insert into test values ('M1','I2');
1 row created.
SQL> insert into test values ('M2','I3');
1 row created.
SQL> insert into test values ('M3','I4');
1 row created.
SQL> insert into test values ('M3','I5');
1 row created.
SQL> select * from test group by mm#,itm#;
MM# IT
M2  I3
M3  I5
M3  I4
M1  I1
M1  I2
SQL> select * from test group by mm#,itm# order by 1;
MM# IT
M1  I1
M1  I2
M2  I3
M3  I4
M3  I5
SQL>HTH
Girish Sharma