1. Index by table
2. Nested Table
3. Varray
4. Records

  

  
Index by table:
  
    declare
      type my_tbl_typ is table of char index by binary_integer;
      my_tbl my_tbl_typ;
    begin
      my_tbl(0):=0;
      my_tbl(1):=1;
      my_tbl(2):=2;
      dbms_output.put_line(my_tbl(2) );
    end;
  
Nested Table
  
    declare
      type my_tbl_typ is table of char;
      my_tbl my_tbl_typ;
    begin
      my_tbl := my_tbl_typ( '0','1','2');
      dbms_output.put_line(my_tbl(2) );
    end;
  
Varray
  
      declare
      type my_tbl_typ is varray(10) of char;
      my_tbl my_tbl_typ;
    begin
      my_tbl := my_tbl_typ( '0','1','2');
      dbms_output.put_line(my_tbl(2) );
    end;
  

  A index by table is initially initialised to null, therefore
  before accessing the element we need to initialise the value.
  If you try to access a value in a index by table which has not
  been assigned a value earlier, we would get a no data found error.
  For example in the above example if we had used
  dbms_output.put_line ( my_tbl(11)) ;
  we would get the no data found error.
  The first element in a index by table gets a subscript of 0.
  Yes the subscript in index by tables can be negative as well.
  my_tbl(-11):=11;
  dbms_output.put_line ( my_tbl(-11)) ;

  Index by table size is not determined at the time of creation
  for example it is perfectly legal to say
  my_tbl(1000):=1000;
  A index by table cannot be stored in the database.



  A nested table and varray are null by default. We have to use a constructor to
  initialise them for example :
  my_tbl := my_tbl_typ( '0','1','2');  
  The first element gets a subscript of 1.
  Which means my_tbl(0) is invalid and my_tbl(1)=>0.
  A nested table and varray by table can be stored in the database.
  

  Assignment :
    Index by tables can be assigned by direct assignment for example
    using the same example as above a index by table assignment can
    be done as:
    declare
	  type my_tbl_typ is table of char index by binary_integer;
	  my_tbl my_tbl_typ;
	  my_tbl_2 my_tbl_typ;
	begin
	  my_tbl(0):=0;
	  my_tbl(1):=1;
	  my_tbl(-11):=2;
	  my_tbl_2:=my_tbl;
	  dbms_output.put_line(my_tbl_2(-11) );
    end;

    A index by table and varray can also be assigned in the same way as
    above.
    

    Caution:Collections (any three of the above) can never be used for comparison directly
    for example a statement such as :
    if ( my_tbl = my_tbl_2 )  --Invalid this will raise a compilation error.
    then
    null;
    end if;
    

    The following are the collection methods:
    EXISTS -- returns true if nth element exists or false.
       IF my_tbl.EXISTS(0) THEN my_tbl(0) := 2; END IF;
    COUNT  -- gives the count of the collection.
       FOR i IN 1..my_tbl.COUNT LOOP 
    LIMIT  -- Max. that an collection can contain, for nested tables returns null.
    FIRST AND LAST -- Return index number in a collection, if uninitalised return null.
    PRIOR AND NEXT  -- Return the preceding and next elements index.
    EXTEND  -- Used to extend a collection in varray. (NOT Applicable to index by table.)
    TRIM  -- Removes n elements from an array.
    DELETE -- DELETE removes all elements from a collection.
    Of the above methods only , EXTEND and TRIM cannot be used with index-by tables

     A record stores a group of elements in a structured format.
     Example:
     Records cannot be tested for nullity, equality, or inequality.
     For instance, the following IF conditions are illegal