Getting index of element in PL/SQL collection - oracle

Question

Is there a built-in function to determine the (first) index of an element in a PL/SQL collection?
Something like
DECLARE
TYPE t_test IS TABLE OF VARCHAR2(1);
v_test t_test;
BEGIN
v_test := NEW t_test('A', 'B', 'A');
dbms_output.put_line( 'A: ' || get_index( v_test, 'A' ) );
dbms_output.put_line( 'B: ' || get_index( v_test, 'B' ) );
dbms_output.put_line( 'C: ' || get_index( v_test, 'C' ) );
END;
A: 1
B: 2
C:
I can use Associative Arrays, Nested Tables or Varrays, whatever necessary. If the same element exists more than once, then the index of the first occurrence is sufficient.
Otherwise I'd have to do something like
CREATE FUNCTION get_index ( in_test IN t_test, in_value IN VARCHAR2 )
RETURN PLS_INTEGER
AS
i PLS_INTEGER;
BEGIN
i := in_test.FIRST;
WHILE( i IS NOT NULL ) LOOP
IF( in_test(i) = in_value ) THEN
RETURN i;
END IF;
i := in_test.NEXT(i);
END LOOP;
RETURN NULL;
END get_index;

Answer 1

Not sure, if this really helps, or if you think it is more elegant:
create type t_test as table of varchar2(1);
/
DECLARE
--TYPE t_test IS TABLE OF VARCHAR2(1);
v_test t_test;
function get_index(q in t_test, c in varchar2) return number is
ind number;
begin
select min(rn) into ind from (
select column_value cv, rownum rn
from table(q)
)
where cv = c;
return ind;
end get_index;
BEGIN
v_test := NEW t_test('A', 'B', 'A');
dbms_output.put_line( 'A: ' || get_index( v_test, 'A' ) );
dbms_output.put_line( 'B: ' || get_index( v_test, 'B' ) );
dbms_output.put_line( 'C: ' || get_index( v_test, 'C' ) );
END;
/
show errors
drop type t_test;

Answer 2

I don't think there is a built-in function that searches a collection. However, if you know you will need to search a collection a lot, you could build an index. Adding element to the collection will be a bit more expensive, but looking for an element will be an O(1) operation (instead of O(n) for a brute force search). For example, you could use something like this:
SQL> DECLARE
2 TYPE t_test IS TABLE OF VARCHAR2(1);
3 TYPE t_test_r IS TABLE OF NUMBER INDEX BY VARCHAR2(1);
4
5 v_test t_test;
6 v_test_r t_test_r;
7
8 FUNCTION get_index(p_test_r t_test_r,
9 p_element VARCHAR2) RETURN NUMBER IS
10 BEGIN
11 RETURN p_test_r(p_element);
12 EXCEPTION
13 WHEN no_data_found THEN
14 RETURN NULL;
15 END get_index;
16
17 PROCEDURE add_element(p_test IN OUT t_test,
18 p_test_r IN OUT t_test_r,
19 p_element VARCHAR2) IS
20 BEGIN
21 p_test.extend;
22 p_test(p_test.count) := p_element;
23 p_test_r(p_element) := least(p_test.count,
24 nvl(get_index(p_test_r, p_element),
25 p_test.count));
26 END add_element;
27 BEGIN
28 v_test := NEW t_test();
29 add_element(v_test, v_test_r, 'A');
30 add_element(v_test, v_test_r, 'B');
31 add_element(v_test, v_test_r, 'A');
32 dbms_output.put_line('A: ' || get_index(v_test_r, 'A'));
33 dbms_output.put_line('B: ' || get_index(v_test_r, 'B'));
34 dbms_output.put_line('C: ' || get_index(v_test_r, 'C'));
35 END;
36 /
A: 1
B: 2
C:
PL/SQL procedure successfully completed
You could also define a record that contains both arrays and all functions/procedures to interact with arrays would use this record type.

Answer 3

When in doubt, consult the documentation ;) (here)
DECLARE
TYPE aa_type_int IS TABLE OF INTEGER INDEX BY PLS_INTEGER;
aa_int aa_type_int;
PROCEDURE print_first_and_last IS
BEGIN
DBMS_OUTPUT.PUT_LINE('FIRST = ' || aa_int.FIRST);
DBMS_OUTPUT.PUT_LINE('LAST = ' || aa_int.LAST);
END print_first_and_last;
BEGIN
aa_int(1) := 3;
aa_int(2) := 6;
aa_int(3) := 9;
aa_int(4) := 12;
DBMS_OUTPUT.PUT_LINE('Before deletions:');
print_first_and_last;
aa_int.DELETE(1);
aa_int.DELETE(4);
DBMS_OUTPUT.PUT_LINE('After deletions:');
print_first_and_last;
END;
/
Result:
Before deletions:
FIRST = 1
LAST = 4
After deletions:
FIRST = 2
LAST = 3