Comments on: NOT IN and NULL

By: Hongfa Wu

Hongfa Wu — Wed, 25 Jun 2008 21:20:40 +0000

Please ignore previous post, this one is correct

———————————————–
select * from dual
WHERE (1) NOT IN (SELECT NULL FROM DUAL);

/*(1) NOT IN (SELECT NULL FROM DUAL)
NOT ( 1 IN (SELECT NULL FROM DUAL))
NOT (1=NULL)
NOT (NULL)
NULL
So return now rows as only True returning rows.*/

select * from dual
WHERE (1,1) NOT IN (SELECT NULL,1 FROM DUAL);

/*(1,1) NOT IN (SELECT NULL,1 FROM DUAL)
NOT ((1,1) IN (SELECT NULL,1 FROM DUAL))
NOT (1=NULL AND 1=1)
NOT (NULL AND TRUE)
NOT (NULL)
NULL
So return now rows as only True returning rows.*/

select * from dual
WHERE (1,1) NOT IN (SELECT NULL,2 FROM DUAL);

/*(1,1) NOT IN (SELECT NULL,2 FROM DUAL)
NOT ((1,1) IN (SELECT NULL,2 FROM DUAL))
NOT (1=NULL AND 1=2)
NOT (NULL AND FALSE)
NOT (FALSE)
TRUE
So return rows.*/

/*The above analysis is based on the fact that:
NULL AND TRUE = NULL (1)
NULL AND FALSE=FALSE (2)
NULL OR TRUE=TRUE (3)
NULL OR FALSE=NULL (4)*/

/*Why is that? Becuase:
For ‘AND’ condition, the whole expression is TRUE only if all of them are TRUE,
otherwise if any of them is FALSE, the whole expression will be FALSE, otherwise is NULL.

TRUE AND TRUE AND TRUE = TRUE
TRUE AND FALSE AND NULL = FALSE
TRUE AND NULL AND FALSE = FALSE
TRUE AND NULL AND NULL = NULL*/

–Examples:

/*TRUE AND TRUE AND TRUE = TRUE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=1) AND (1=1);
–return 1 row
/*TRUE AND FALSE AND NULL = FALSE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=2) AND (1=NULL);
–return no row

/*Not(TRUE AND FALSE AND NULL) = NOT (FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=2) AND (1=NULL));
–return 1 row

/*TRUE AND NULL AND FALSE = FALSE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=null) AND (1=2);
–return no row

/*NOT(TRUE AND NULL AND FALSE) = NOT(FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=null) AND (1=2));
–return 1 row

/*NOT(TRUE AND NULL AND NULL) = NOT(NULL)=NULL*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=null) AND (1=null));
–return no row

/*For ‘OR’ condition, the whole expression is FALSE if all of them are FALSE,
otherwise if any of them is TRUE, the whole expression is TRUE, otherwise is NULL.

FALSE OR FALSE OR FALSE = FALSE
FALSE OR TRUE OR NULL = TRUE
FALSE OR NULL OR TRUE = TRUE
FALSE OR NULL OR NULL = NULL*/

–For examples:
/*FALSE OR FALSE OR FALSE = FALSE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=2) OR (1=2);
–return no row

/*NOT(FALSE OR FALSE OR FALSE) = NOT(FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=2) OR (1=2) OR (1=2));
–return 1 row

/*FALSE OR TRUE OR NULL = TRUE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=1) OR (1=NULL);
–return 1 row

/*FALSE OR NULL OR TRUE = TRUE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=NULL) OR (1=1);
–return 1 row

/*FALSE OR NULL OR NULL = NULL*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=null) OR (1=null);
–return no row

/*NOT(FALSE OR NULL OR NULL) = NOT(NULL)=NULL*/
SELECT * FROM DUAL
WHERE NOT((1=2) OR (1=null) OR (1=null));
–return no row

By: Hongfa Wu

Hongfa Wu — Wed, 25 Jun 2008 20:47:56 +0000

select * from dual
WHERE (1) NOT IN (SELECT NULL FROM DUAL);

(1) NOT IN (SELECT NULL FROM DUAL)
NOT ( 1 IN (SELECT NULL FROM DUAL))
NOT (1=NULL)
NOT (NULL)
NULL
So return now rows as only True returning rows.

select * from dual
WHERE (1,1) NOT IN (SELECT NULL,1 FROM DUAL);

(1,1) NOT IN (SELECT NULL,1 FROM DUAL)
NOT ((1,1) IN (SELECT NULL,1 FROM DUAL))
NOT (1=NULL AND 1=1)
NOT (NULL AND TRUE)
NOT (NULL)
NULL
So return now rows as only True returning rows.

select * from dual
WHERE (1,1) NOT IN (SELECT NULL,2 FROM DUAL);

(1,1) NOT IN (SELECT NULL,2 FROM DUAL)
NOT ((1,1) IN (SELECT NULL,2 FROM DUAL))
NOT (1=NULL AND 1=2)
NOT (NULL AND FALSE)
NOT (FALSE)
TRUE
So return rows.

The above analysis is based on the fact that:
NULL AND TRUE = NULL (1)
NULL AND FALSE=FALSE (2)
NULL OR TRUE=TRUE (3)
NULL OR FALSE=NULL (4)

Why is that?
For ‘AND’ condition, the whole expression is TRUE only if all of them are TRUE, otherwise if any of them is FALSE, the whole expression will be FALSE, otherwise is NULL.
So, TRUE AND TRUE AND TRUE = TRUE
TRUE AND FALSE AND NULL = FALSE
TRUE AND NULL AND FALSE = FALSE
TRUE AND NULL AND NULL = NULL
Examples:
/*TRUE AND TRUE AND TRUE = TRUE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=1) AND (1=1);
–return 1 row
/*TRUE AND FALSE AND NULL = FALSE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=2) AND (1=NULL);
–return no row

/*Not(TRUE AND FALSE AND NULL) = NOT (FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=2) AND (1=NULL));
–return 1 row

/*TRUE AND NULL AND FALSE = FALSE*/
SELECT * FROM DUAL
WHERE (1=1) AND (1=null) AND (1=2);
–return no row

/*NOT(TRUE AND NULL AND FALSE) = NOT(FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=null) AND (1=2));
–return 1 row

/*NOT(TRUE AND NULL AND NULL) = NOT(NULL)=NULL*/
SELECT * FROM DUAL
WHERE NOT((1=1) AND (1=null) AND (1=null));
–return no row

For ‘OR’ condition, the whole expression is FALSE if any of them is FALSE, otherwise if all of them is TRUE, the whole expression is TRUE, otherwise is NULL.
So, TRUE OR FALSE OR NULL =FALSE
FALSE OR TRUE OR NULL = FALSE
TRUE OR NULL OR TRUE = NULL
TRUE OR TRUE OR TRUE = TRUE

For examples:
/*FALSE OR FALSE OR FALSE = FALSE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=2) OR (1=2);
–return no row

/*NOT(FALSE OR FALSE OR FALSE) = NOT(FALSE)=TRUE*/
SELECT * FROM DUAL
WHERE NOT((1=2) OR (1=2) OR (1=2));
–return 1 row

/*FALSE OR TRUE OR NULL = TRUE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=1) OR (1=NULL);
–return 1 row

/*FALSE OR NULL OR TRUE = TRUE*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=NULL) OR (1=1);
–return 1 row

/*FALSE OR NULL OR NULL = NULL*/
SELECT * FROM DUAL
WHERE (1=2) OR (1=null) OR (1=null);
–return no row

/*NOT(FALSE OR NULL OR NULL) = NOT(NULL)=NULL*/
SELECT * FROM DUAL
WHERE NOT((1=2) OR (1=null) OR (1=null));
–return no row

Why is that? Because

By: Laurent Schneider

Laurent Schneider — Wed, 07 Nov 2007 08:42:18 +0000

one more plan


var a number
var b number
var w number
var x number
var y number
var z number
select * from dual where (:a,:b) not in ((:w,:x),(:y,:z));

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter((:Z<>B OR :Y<>A) AND (:X<>:B OR :W<>:A))

By: Laurent Schneider

Laurent Schneider — Thu, 01 Nov 2007 08:46:06 +0000

Thanks for the hint of looking at the explain plan filter.

If you try with something else than litteral, you would get a LNNVL


SQL> select /*+ RULE */ * from t1 where (a,b) not in (select c,d from t2);

no rows selected

Execution Plan
----------------------------------------------------------
Plan hash value: 3597920939

-----------------------------------
| Id  | Operation          | Name |
-----------------------------------
|   0 | SELECT STATEMENT   |      |
|*  1 |  FILTER            |      |
|   2 |   TABLE ACCESS FULL| T1   |
|*  3 |   TABLE ACCESS FULL| T2   |
-----------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   1 - filter( NOT EXISTS (SELECT 0 FROM "T2" "T2" WHERE
              LNNVL("D"<>:B1) AND LNNVL("C"<>:B2)))
   3 - filter(LNNVL("D"<>:B1) AND LNNVL("C"<>:B2))

Note
-----
   - rule based optimizer used (consider using cbo)

By: Chris

Chris — Wed, 31 Oct 2007 22:08:44 +0000

Running it through explain plan comes up with interesting filter predicates (10.2.0.3):

1 - filter( NOT EXISTS (SELECT /*+ */ 0 FROM “DUAL” “DUAL” WHERE
NULL IS NOT NULL))
3 - filter(NULL IS NOT NULL)

By: ittichai

ittichai — Wed, 31 Oct 2007 15:18:45 +0000

My 2-cent is that any comparison with NULL actually does not yield anything simply because it could not be done. A NULL (not defined) cannot be compared or calculated. I see NULL as a state. That’s why it can be only be used with IS or IS NOT.

Laurent, I agree with your assumption. Since the first comparison a!=c is not comparable due to value NULL is involved, so, I assume, it is ignored. However, the second comparison b!=d return TRUE, and that counts.

Thanks for provoking our thinking.

By: Laurent Schneider

Laurent Schneider — Wed, 31 Oct 2007 13:06:29 +0000

the point is :

(1,1) NOT IN (SELECT NULL,2 FROM DUAL);

returns TRUE

also note that Any comparison between null and another value will return false is inaccurate.


begin
  case (1=null) 
    when TRUE then 
      dbms_output.put_line('true');
    when FALSE then 
      dbms_output.put_line('false'); 
    else 
      dbms_output.put_line('Not TRUE and not FALSE'); 
  end case;
end;
/

Not TRUE and not FALSE

By: Quique

Quique — Wed, 31 Oct 2007 11:00:07 +0000

Any comparison between null and another value will return false, unless the operators are used is null or is not null