TRIM method

The TRIM method is used to remove elements from the end of a varray or nested table.

The usage of the TRIM method is described as follows:

• The TRIM method removes one element from the end of a collection. Therefore, the collection must contain at least one element; otherwise, the predefined exception SUBSCRIPT_BEYOND_COUNT will be raised.

• The TRIM(n) method removes n elements from the end of a collection. Therefore, the collection must contain at least n elements; otherwise, the predefined exception SUBSCRIPT_BEYOND_COUNT will be raised.

The TRIM method operates based on the internal size of the collection. In other words, if the DELETE method removes an element but leaves a placeholder for it, the TRIM method considers the element to still exist. Therefore, the TRIM method can remove elements that have been deleted.

PL/SQL does not retain placeholders for trimmed elements. Therefore, trimmed elements are not included in the internal size of the collection, and you cannot restore trimmed elements by assigning valid values to them.

Here is an example:

obclient> DECLARE
  t nested_type:= nested_type('A', 'B', 'C', 'D', 'E', 'F');
BEGIN
  print_t(t);

  t.TRIM;          -- Trim the last element.
  print_t(t);

  t.DELETE(3);     -- Delete the third element.
  print_t(t);

  t.TRIM(2);       -- Trim the last two elements.
  print_t(t);

END;
/
Query OK, 0 rows affected

t.(1) = A
t.(2) = B
t.(3) = C
t.(4) = D
t.(5) = E
t.(6) = F
---
t.(1) = A
t.(2) = B
t.(3) = C
t.(4) = D
t.(5) = E
---
t.(1) = A
t.(2) = B
t.(4) = D
t.(5) = E
---
t.(1) = A
t.(2) = B
---

In this example, a nested table variable is declared and initialized with six elements. The following operations are performed:

1. Trim the last element.

2. Delete the fourth element.

3. Trim the last two elements.

The print_nt stored procedure outputs the nested table variable after initialization and after the TRIM and DELETE operations.