select *
  from xmltable('/VALUE'
                passing xmltype('<VALUE>qwerty</VALUE>')
                columns value varchar2(30) path '/VALUE')
 where :x = 1;

select *
  from xmltable('/VALUE'
                passing xmltype('<VALUE>qwerty</VALUE>')
                columns value /*varchar2(30)*/ path '/VALUE')
 where :x = 1;

/* Formatted on 26.02.2014 13:11:16 (QP5 v5.256.13226.35510) */
SELECT *
  FROM (SELECT *
          FROM (SELECT *
                  FROM (SELECT * FROM DUAL) b) c) d

BEGIN
   FOR i IN 1 .. 2
   LOOP
      FOR i IN 1 .. 2
      LOOP
         FOR i IN 1 .. 2
         LOOP
            NULL;
         END LOOP; END LOOP; END LOOP; END;

SELECT OWNER,
       TABLE_NAME,
       TABLESPACE_NAME,
       CLUSTER_NAME,
       IOT_NAME,
       PCT_FREE,
       PCT_USED,
       INI_TRANS,
       MAX_TRANS,
       INITIAL_EXTENT,
       NEXT_EXTENT,
       MIN_EXTENTS,
       MAX_EXTENTS,
       PCT_INCREASE
  FROM SYS.ALL_TABLES;

и 

SELECT DISTINCT OWNER,
                TABLE_NAME,
                TABLESPACE_NAME,
                CLUSTER_NAME,
                IOT_NAME,
                PCT_FREE,
                PCT_USED,
                INI_TRANS,
                MAX_TRANS,
                INITIAL_EXTENT,
                NEXT_EXTENT,
                MIN_EXTENTS,
                MAX_EXTENTS,
                PCT_INCREASE
  FROM SYS.ALL_TABLES;

select ***
  from table a,
       table b,
       table c
 where c... = b...