Eddie Awad’s Blog - Latest Comments in Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Laurent Schneider — Thu, 06 Dec 2007 11:26:57 -0000

I tried

select * from dual where sys_op_map_nonnull(null) = 'FF' ;
D
-
X

It does return a row on my 10.2.0.3

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Michael Friedman — Mon, 25 Sep 2006 21:18:47 -0000

Whoa.

Am I confused?

I thought sys_op_map_nonnull('any non-null value') was supposed be 'any non-null value'.

I can also guarantee to you that

select *
from dual
where sys_op_map_nonnull(null) = 'FF'

returns a row.

Now I think it's doing something more subtle - it's doing a mapping of anything you put in it so

select *
from dual
where sys_op_map_nonnull(null) = sys_op_map_nonnull('FF')

will not return a row... need to test.

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Eddie Awad — Mon, 25 Sep 2006 20:16:05 -0000

Jonathan, thanks for clarifying the subtlety of sys_op_map_nonnull.

Here is a quick test that I think demonstrates Michael's point that sys_op_map_nonnull (col1) is the same as nvl(col1,'FF'):

  EDDIE@XE> CREATE TABLE t (
    2   col1  VARCHAR2(10),
    3   col2  VARCHAR2(10));

  Table created.

  EDDIE@XE> INSERT INTO t
    2       VALUES (NULL,
    3               NULL
    4              )
    5  /

  1 row created.

  EDDIE@XE> INSERT INTO t
    2       VALUES ('FF',
    3               'FF'
    4              )
    5  /

  1 row created.

  EDDIE@XE> INSERT INTO t
    2       VALUES ('Eddie',
    3               'Awad'
    4              )
    5  /

  1 row created.

  EDDIE@XE> SELECT NVL (col1, 'I am null') col1,
    2         NVL (col2, 'I am null') col2
    3    FROM t
    4   WHERE nvl(col1,'FF') = nvl(col2,'FF')
    5  /

  COL1       COL2
  ---------- ----------
  I am null  I am null
  FF         FF

  EDDIE@XE> SELECT NVL (col1, 'I am null') col1,
    2         NVL (col2, 'I am null') col2
    3    FROM t
    4   WHERE sys_op_map_nonnull (col1) = sys_op_map_nonnull (col2)
    5  /

  COL1       COL2
  ---------- ----------
  I am null  I am null
  FF         FF

So, if sys_op_map_nonnull (col1) did not act like nvl(col2,'FF'), Oracle would not return the row with the varchar2 value FF in both col1 and col2.

I think the explanation here is that sys_op_map_nonnull ('FF') equals sys_op_map_nonnull ('FF') but sys_op_map_nonnull ('FF') does not equal 'FF':

  EDDIE@XE> SELECT *
    2  FROM dual
    3  where  sys_op_map_nonnull ('FF') = sys_op_map_nonnull ('FF')
    4  /

  D
  -
  X

  EDDIE@XE> SELECT *
    2  FROM dual
    3  where  sys_op_map_nonnull ('FF') = 'FF'
    4  /

  no rows selected

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Jonathan Lewis — Mon, 25 Sep 2006 17:48:18 -0000

sys_op_map_nonnull() is a little more subtle than nvl(x,'0xff').

The thing it maps to is an internally stored FF, and I don't think you can get this actual value stored for any type except RAW. Then, to deal with the problem of comparing raws when using sys_op_mapnonnull(), sys_op_mapnonnull(ff) returns a two-byte value which is 00ff, so sys_op_map_nonnull(ff) != ff.

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Eddie Awad — Wed, 20 Sep 2006 12:39:16 -0000

Michael, I guess you have just found out why it's not documented. There are many other ways to compare two nulls, so there is really no need to use sys_op_map_nonnull. However, I will always be interested in the "undocumented", just to satisfy my curiosity.

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Michael Friedman — Wed, 20 Sep 2006 08:02:04 -0000

This would be a lot more interesting if it did not just act like nvl(x,'FF'). What's the point? You could have FF in your data.

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Eddie Awad — Wed, 20 Sep 2006 00:29:56 -0000

Thanks for the extra tip Pete.

Re: Cool Undocumented SQL Function SYS_OP_MAP_NONNULL and Some Alternatives

Pete_s — Tue, 19 Sep 2006 11:46:46 -0000

Oracle uses this function in the 'default' index on materialized views for fast refresh - which in the case of DW Mviews is a little odd as I would not expect NULLS in my fact summaries!