Using RowID to get the first instance of a value in a table

Question

I have a table of the structure
SECURITY(
COMPANY_ID NUMBER,
SECURITY_ID NUMBER,
CUSIP
One company can have many CUSIPs asociated with it and I want to find the best way to find any valid CUSIP for the company_id using PL/SQL.
Here is my approach, I would like any other suggestions or comments.
SELECT
rowid INTO v_row_id
FROM
SECURITY
where COMPANY_ID=v_company_id
and rownum<2
SELECT
CUSIP INTO v_cusip
FROM
SECURITY
where rowid=v_row_id

Answer 1

Hello
If you don't specify an order you will let oracle decide what the "first" row is. It may be the first row that was inserted, it could be the last, or it could be any other row for that company. If the execution plan for the query changes (or a number of other things) the first row returned could change. This may of course not matter to you at all but it's worth pointing out I think:
create table dt_test_SECURITY(
COMPANY_ID NUMBER,
SECURITY_ID NUMBER,
CUSIP varchar2(20)
--generate some test data
SQL> insert into dt_test_security select mod(rownum,200)+1,mod(rownum,10)+1,to_char(rownum) from dba_objects where rownum <2001;
2000 rows created.
SQL>
SQL> SELECT
  2     CUSIP
  3  FROM
  4     dt_test_SECURITY
  5  where
  6     COMPANY_ID=1;
CUSIP
2000
200
400
600
800
1000
1200
1400
1600
1800
10 rows selected.
SQL> SELECT
  2     CUSIP
  3  FROM
  4     dt_test_SECURITY
  5  where
  6     COMPANY_ID=1
  7  and
  8     rownum<2;
CUSIP
2000
create index dt_test_security_idx2 on dt_test_security(company_id,cusip);
exec dbms_stats.gather_table_stats(ownname=>user,tabname=>'DT_TEST_SECURITY',method_opt=>'FOR TABLE FOR ALL INDEXES FOR ALL INDEXED COLUMNS');
SQL> SELECT
  2     CUSIP
  3  FROM
  4     dt_test_SECURITY
  5  where
  6     COMPANY_ID=1;
CUSIP
1000
1200
1400
1600
1800
200
2000
400
600
800
SQL> SELECT
  2     CUSIP
  3  FROM
  4     dt_test_SECURITY
  5  where
  6     COMPANY_ID=1
  7  and
  8     rownum<2;
CUSIP
1000If you use MAX(cusip), you will get the highest cusip against the company which is much more specific. Is that what you want? How are you intend to determin which is the first row, or doesn't it matter?
HTH
David