To enlarge the size of a collection, use EXTEND. This process has 3 forms. The EXTEND appends one null element to a collection. And the EXTEND(n) appends n null elements to a collection. EXTEND(n,i) appends n copies of the ith element to the collection. For e.g. the statement below appends 5 copies of element 1 to nested table courses:
You cannot use the EXTEND to initialize an automatically null collection. In addition if you impose the NOT NULL constraint on a TABLE or VARRAY type, you cannot apply the first two forms of EXTEND to collections of that kind.
The EXTEND operates on the internal size of the collection, that includes any deleted elements. Therefore, if EXTEND encounters deleted the elements, then it includes them in its tally. The PL/SQL keeps placeholders for the deleted elements so that you can swap them whenever you wish. Consider the example shown below:
TYPE CourseList IS TABLE OF VARCHAR2(10);
courses := CourseList('Biol 4412', 'Psyc 3112', 'Anth 3001');
courses.DELETE(3); -- delete element 3
/* PL/SQL keeps a placeholder for element 3. So, the
next statement appends element 4, not element 3. */
courses.EXTEND; -- append one null element
/* Now element 4 exists, so the next statement does
not raise SUBSCRIPT_BEYOND_COUNT. */
courses(4) := 'Engl 2005';
Whenever it includes deleted elements, then the internal size of a nested table differs from the values returned by the COUNT and LAST. For illustration, when you initialize a nested table with five elements, delete the elements 2 & 5, then the internal size is 5, and the COUNT returns 3, & the LAST returns 4. All the deleted elements are treated similarly.