PLSQL Index-By Tables:

===============
The first type of collection is known as index-by tables. These behave in the same way as arrays except that have no upper bounds,
 allowing them to constantly extend. As the name implies, the collection is indexed using BINARY_INTEGER values, which do not need to be consecutive.
The collection is extended by assigning values to an element using an index value that does not currently exist.

sql>SET SERVEROUTPUT ON SIZE 1000000
sql>DECLARE
  TYPE table_type IS TABLE OF NUMBER(10)
    INDEX BY BINARY_INTEGER;
 
  v_tab  table_type;
  v_idx  NUMBER;
BEGIN
  -- Initialise the collection.
  << load_loop >>
  FOR i IN 1 .. 5 LOOP
    v_tab(i) := i;
  END LOOP load_loop;
 
  -- Delete the third item of the collection.
  v_tab.DELETE(3);
 
  -- Traverse sparse collection
  v_idx := v_tab.FIRST;
  << display_loop >>
  WHILE v_idx IS NOT NULL LOOP
    DBMS_OUTPUT.PUT_LINE('The number ' || v_tab(v_idx));
    v_idx := v_tab.NEXT(v_idx);
  END LOOP display_loop;
END;
/


Ur's
AmarAlam