Associative Array vs Table Scan

Question

Still new to PL/SQL, but very keen to learn. I wondered if somebody could advise me whether I should use a collection (such as an associative array) instead of repeating a table scan within a loop for the example below. I need to read from an input table of experiment data and if the EXPERIMENT_ID does not already exist in my EXPERIMENTS table, then add it. Here is the code I have so far. My instinct is that it my code is inefficient. Would it be more efficient to scan the EXPERIMENTS table only once and store the list of IDs in a collection, then scan the collection within the loop?
-- Create any new Experiment IDs if needed
open CurExperiments;
loop
-- Fetch the explicit cursor
fetch CurExperiments
into vExpId, dExpDate;
exit when CurExperiments%notfound;
-- Check to see if already exists
select count(id)
into iCheckExpExists
from experiments
where id = vExpId;
if iCheckExpExists = 0 then
-- Experiment ID is not already in table so add a row
insert into experiments
(id, experiment_date)
values(vExpId, dExpDate);
end if;
end loop;

Answer 1

Except that rownum is assigned after the result set
is computed, so the whole table will have to be
scanned.really?
SQL> explain plan for select * from i;
Explained.
SQL> select * from table( dbms_xplan.display );
PLAN_TABLE_OUTPUT
Plan hash value: 1766854993
| Id  | Operation         | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT  |      |   910K|  4443K|   630   (3)| 00:00:08 |
|   1 |  TABLE ACCESS FULL| I    |   910K|  4443K|   630   (3)| 00:00:08 |
8 rows selected.
SQL> explain plan for select * from i where rownum=1;
Explained.
SQL> select * from table( dbms_xplan.display );
PLAN_TABLE_OUTPUT
Plan hash value: 2766403234
| Id  | Operation          | Name | Rows  | Bytes | Cost (%CPU)| Time     |
|   0 | SELECT STATEMENT   |      |     1 |     5 |     2   (0)| 00:00:01 |
|*  1 |  COUNT STOPKEY     |      |       |       |            |          |
|   2 |   TABLE ACCESS FULL| I    |     1 |     5 |     2   (0)| 00:00:01 |
Predicate Information (identified by operation id):
   1 - filter(ROWNUM=1)
14 rows selected.