PIVOT and UNPIVOT

PIVOT:

 select * from
 (
     (
        select 'a' value  from dual union all
        select 'e' value  from dual union all
        select 'i'  value  from dual union all
        select 'o' value  from dual union all
        select 'u' value  from dual
    )
   pivot  -- use pivot xml to get the o/p in xml
    (
       count( value)
       for value in   ('a','e','i','o','u')
    )
 )

UNPIVOT:

 select value from
 (
    (
        select
            'a' v1,
            'e' v2,
            'i' v3,
            'o' v4,
            'u' v5
        from dual
    )
    unpivot [INCLUDE NULLS]
    (
        value
        for value_type in
            (v1, v2,v3,v4,v5) – Also can give ANY here.
    )
 )