TRIM method

The TRIM method is used to remove elements from the end of a variable-length array or nested table.

The TRIM method is used 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 is 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 is 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;          -- Trims the last element
  print_t(t);

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

  t.TRIM(2);       -- Trims 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. The last element is trimmed.

2. The fourth element is deleted.

3. The last two elements are trimmed.

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