Oracle TRIM method

In Oracle PL/SQL TRIM method removes all items from any collection type. This operation immediately frees up the memory allocated to the items to be removed.

Syntax of TRIM collection method in Oracle PL/SQL

collect_name_id.TRIM;
collect_name_id.TRIM (n);

Parameters or arguments

• collect_name_id – is the name of the collection.
• TRIM – removes one element from the end of the collection if the collection has at least one element.
• TRIM (n) – removes n items from the end of the collection if the collection has at least n items at the end.

If there are no items in the collection, the predefined exception SUBSCRIPT_BEYOND_COUNT is called.

TRIM works with the internal size of the collection. That is, if DELETE deletes an item but saves its filler, TRIM considers that this item exists. Therefore TRIM can remove the removed item.

PL/SQL does not hold a filler for the clipped items. Therefore, the cropped items are not part of the internal size of the collection, and you cannot recover the cropped item by assigning it a valid value.

TRIM works with the internal size of the collection. That is, if DELETE deletes an item but saves its filler, TRIM assumes that the item exists. So TRIM can remove the removed item.

PL/SQL does not hold a filler for the trimmed items. Therefore, the cropped items are not part of the internal size of the collection, and you cannot recover the cropped item by assigning it a valid value.

Do not rely on interactions between TRIM and DELETE. Process Nested Tables as varray arrays (and use only DELETE) or stacks (and use only TRIM and EXTEND).

Consider an example to understand how to use the TRIM collection method in Oracle PL/SQL.

Example of TRIM with Nested Tables

Let’s consider an example where we declare the Nested Tables variable:

The print_nt_id procedure prints the nested table variable after initialization and after TRIM and DELETE operations.

CREATE OR REPLACE TYPE nt_type_id IS TABLE OF NUMBER;

CREATE OR REPLACE PROCEDURE print_nt_id (nt nt_type_id) IS
i NUMBER;
BEGIN
i := nt.FIRST;

IF i IS NULL THEN
DBMS_OUTPUT.PUT_LINE('nt is empty');
ELSE .
WHILE i IS NOT NULL LOOP
DBMS_OUTPUT.PUT('nt.(' || i || ') = '); print(nt(i));
i := nt.NEXT(i);
END LOOP;
END IF;

DBMS_OUTPUT.PUT_LINE('---');
END print_nt_id;

DECLARE
nt nt_type_id := nt_type_id(11, 22, 33, 44, 55, 66);
BEGIN
print_nt_id(nt);

nt.TRIM; -- Cuts off the last element
print_nt_id(nt);

nt.DELETE(4); -- Delete the fourth element
print_nt_id(nt);

nt.TRIM(2); -- Cuts off the last two elements
print_nt_id(nt);
END;

Result:

nt_id.(1) = 11
nt_id.(2) = 22
nt_id.(3) = 33
nt_id.(4) = 44
nt_id.(5) = 55
nt_id.(6) = 66
---
nt_id.(1) = 11
nt_id.(2) = 22
nt_id.(3) = 33
nt_id.(4) = 44
nt_id.(5) = 55
---
nt_id.(1) = 11
nt_id.(2) = 22
nt_id.(3) = 33
nt_id.(5) = 55
---
nt_id.(1) = 11
nt_id.(2) = 22
nt_id.(3) = 33
—

PL/SQL Collection Method TRIM in Oracle Database