Comments on: NVL2()

By: Jonathan Lewis

Jonathan Lewis — Mon, 30 Apr 2012 14:32:20 +0000

Thanks for the responses everyone.

This is one reason why I like the blogging environment to the old Web Page approach. It allows other people to add value to the original article and reveal extra benefits (or problems, or version-dependencies) that you wouldn’t necessarily find out for yourself until it’s too late.

By: jgarry

jgarry — Tue, 24 Apr 2012 20:58:46 +0000

Also more useful if they work. See MOS Bug 5490501 - Wrong Results with COALESCE or NVL2 on aggregations inside subqueries [ID 5490501.8] The wrap issue is explained in How to Find out the Reason for PLS-00201 in PL/SQL [ID 269973.1]: "Some recent SQL syntax is not supported by the wrap utility by default. To enable the support for all SQL syntax, specify the option edebug=wrap_new_sql (with no dash). "

By: Raj

Raj — Tue, 24 Apr 2012 10:25:19 +0000

@Kieran,

I never seem to have any problems with nvl2 apart from the fact that nvl2 is not supported in a pl/sql context for some reason.

3:1051:45945:11234>select * from v$version;


BANNER

--------------------------------------------------------------------------------

Oracle Database 11g Enterprise Edition Release 11.1.0.7.0 - 64bit Production

PL/SQL Release 11.1.0.7.0 - Production

CORE    11.1.0.7.0      Production

TNS for Linux: Version 11.1.0.7.0 - Production

NLSRTL Version 11.1.0.7.0 - Production
3:1051:45945:11234>@ c:\work\sql_scripts\t.sql
Function created.
3:1051:45945:11234>select text from user_Source where name = 'TEST_FUNC';
TEXT

----------------------------------------------------------------------------------------------------

function test_func(pi_input Varchar2)

return varchar2

is

   l_Status Varchar2(10);

Begin

   select nvl2(pi_input, 'Not Null', 'Null') into l_status

   from dual;

   return l_Status;

end;
9 rows selected.
3:1051:45945:11234>select test_func(null) from dual;
TEST_FUNC(NULL)

----------------------------------------------------------------------------------------------------

Null
C:\work\sql_scripts>wrap iname=t.sql oname=t.plb
PL/SQL Wrapper: Release 10.2.0.1.0- Production on Tue Apr 24 11:18:34 2012
Copyright (c) 1993, 2004, Oracle.  All rights reserved.
Processing t.sql to t.plb
3:1051:45945:11234>@ c:\work\sql_scripts\t.plb
Function created.
3:1051:45945:11234>select text from user_Source where name = 'TEST_FUNC';
TEXT

----------------------------------------------------------------------------------------------------

function test_func wrapped

snipped
3:1051:45945:11234>select test_func(null) from dual;
TEST_FUNC(NULL)

----------------------------------------------------------------------------------------------------

Null
3:1051:45945:11234>select test_func('hello') from dual;
TEST_FUNC('HELLO')

----------------------------------------------------------------------------------------------------

Not Null
3:1051:45945:11234>

Thanks

By: Kieran Walsh

Kieran Walsh — Mon, 23 Apr 2012 20:57:55 +0000

I fell in love with NVL2 for about a week – and then realised that it wasn’t a supported construct under the WRAP tool, so it was back to decodes. Sigh.

By: Sayan Malakshinov

Sayan Malakshinov — Mon, 23 Apr 2012 19:39:45 +0000

The nvl2 function is really more appropriate for such fbi in fact, since it is faster than the “decode (x, null, 1)” and, although a little slower than the “case when x is null then 1 end”, but more readable and shorter.

with gen as (
            select n
            from (select level from dual connect by level<=1e6)
                ,(select 1 n from dual
                  union all 
                  select null from dual
                 ) t
)
select sum(nvl2(n,null,1))                 --1.046 secs
       --sum(decode(n,null,1))               -- 1.482 secs
       --sum(case when n is null then 1 end) --0.982 seconds
from gen
/

But it also has disadvantages. For example, in contrast to “decode” it evaluates all its arguments.