Comments on: NVL, NVL2 or COALESCE?

By: Eddie Awad

Eddie Awad — Fri, 06 Oct 2006 04:59:15 +0000

No, nvl is not limited to select statements.
For example: insert into t (comm) values (nvl(mycomm, 0))

By: sumanth

sumanth — Fri, 29 Sep 2006 06:47:41 +0000

how to use nvl function and insert statement together… or… usage of nvl is limited to select statements.. please help

By: Eddie Awad

Eddie Awad — Fri, 27 Jan 2006 23:46:10 +0000

In certain situations in 8i, COALESCE did not behave the same as NVL, in fact it errored out. An example:

user@8i> create table t (id int, f blob)
  2  /

Table created.

user@8i> insert into t (id) values (1)
  2  /

1 row created.

user@8i> select
  2      id
  3      ,dbms_lob.getlength(f)
  4      ,nvl(dbms_lob.getlength(f),0)
  5  from t
  6  /

        ID DBMS_LOB.GETLENGTH(F) NVL(DBMS_LOB.GETLENGTH(F),0)
---------- --------------------- ----------------------------
         1                                                  0

user@8i> select
  2      id
  3      ,dbms_lob.getlength(f)
  4      ,coalesce(dbms_lob.getlength(f),0)
  5  from t
  6  /
    ,coalesce(dbms_lob.getlength(f),0)
     *
ERROR at line 4:
ORA-00904: invalid column name

The above worked in 9i (and XE)

user@9i> create table t (id int, f blob)
  2  /

Table created.

user@9i> insert into t (id) values (1)
  2  /

1 row created.

user@9i> select
  2      id
  3      ,dbms_lob.getlength(f)
  4      ,nvl(dbms_lob.getlength(f),0)
  5  from t
  6  /

        ID DBMS_LOB.GETLENGTH(F) NVL(DBMS_LOB.GETLENGTH(F),0)
---------- --------------------- ----------------------------
         1                                                  0

user@9i> select
  2      id
  3      ,dbms_lob.getlength(f)
  4      ,coalesce(dbms_lob.getlength(f),0)
  5  from t
  6  /

        ID DBMS_LOB.GETLENGTH(F) COALESCE(DBMS_LOB.GETLENGTH(F),0)
---------- --------------------- ---------------------------------
         1                                                       0

By: gsalem

gsalem — Fri, 27 Jan 2006 22:53:03 +0000

Robert,
I think that the difference in perf mentionned on donald’s site (oracledba) is mostly due to the operations used in the tests other than the first one (e.g. nvl(c,to_date(’0001′,’yyyy’)) != nvl(d,to_date(’0001′,’yyyy’)) where the to_date costs a lot). If you workaround these, then the timing differences are much less important.
rgds

By: Robert Vollman

Robert Vollman — Fri, 27 Jan 2006 22:16:52 +0000

I believe this is the article to which David is referring:

http://www.oracledba.co.uk/tips/plsql_nvl_costs.htm

I remember there being another, but I can’t find it.

For the record, I use coalesce in Sybase, but in Oracle that’s the one I don’t use. Don’t know why. Probably DECODE is the one I use the most.

By: David Aldridge

David Aldridge — Fri, 27 Jan 2006 17:12:20 +0000

I remember reading recently (on Ask Tom I believe) that Nvl() has the disadvantage that expr2 is always evaluated even when expr1 is not null, which can be expensive if expr2 is non-trivial -- a PL/SQL function call for example.

That makes Coalesce the winner for me.

By: Karl

Karl — Fri, 27 Jan 2006 15:51:07 +0000

Hey guys!
be honest - i don not beleave that 60% used coalesce?
i always used nvl- the classic NULL -killer Karl

By: Laurent Schneider

Laurent Schneider — Fri, 27 Jan 2006 15:20:07 +0000

(maybe more?)

select decode(x,0,null,x) from t;

select nullif(x,0) from t;