Comments on: NVL, ISNULL, IFNULL and COALESCE http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/ cat /dev/random Sat, 04 Jul 2009 08:07:38 +0000 http://wordpress.org/?v=2.9-rare hourly 1 By: Thorsten Kettner http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/comment-page-1/#comment-144960 Thorsten Kettner Tue, 20 Mar 2007 12:20:18 +0000 http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/#comment-144960 Alistair, you are confusing DECODE and COALESCE. What you describe is the DECODE function. COALESCE works in Oracle as in other dbms. It takes the first value from the list which is not null. Hence giving it two args only equals NVL. Thorsten. Alistair, you are confusing DECODE and COALESCE. What you describe is the DECODE function. COALESCE works in Oracle as in other dbms. It takes the first value from the list which is not null. Hence giving it two args only equals NVL.

Thorsten.

]]> By: Alistair http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/comment-page-1/#comment-123061 Alistair Thu, 22 Feb 2007 13:06:18 +0000 http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/#comment-123061 Joseph, I'm not sure if you're aware or not but there is a difference between an NVL and a COALESCE in Oracle. Using an NVL, you check a single field and replace a NULL value with your preferred replacement, for example: <code>SELECT NVL(dog, 'cat') FROM Animals;</code> In which case, if the dog column contained a NULL value the value of 'cat' would be substituted in. A COALESCE is essentially an inline if-then-elsif-else block. The COALESCE function can accept any number of values and do the replacement, for example: <code>SELECT COALESCE(dog, 'foxy', 'energetic', 'poodle', 'happy', 'cats win') FROM Animal;</code> In the above example, if the value of the dog column is 'foxy', then 'energetic' will be substituted in; likewise for 'poodle' and 'happy'. If it isn't either of those values though, then 'cats win' will be substituted in. Regards, Al. Joseph,

I’m not sure if you’re aware or not but there is a difference between an NVL and a COALESCE in Oracle. Using an NVL, you check a single field and replace a NULL value with your preferred replacement, for example:

SELECT NVL(dog, 'cat') FROM Animals;

In which case, if the dog column contained a NULL value the value of ‘cat’ would be substituted in.

A COALESCE is essentially an inline if-then-elsif-else block. The COALESCE function can accept any number of values and do the replacement, for example:

SELECT COALESCE(dog, 'foxy', 'energetic', 'poodle', 'happy', 'cats win') FROM Animal;

In the above example, if the value of the dog column is ‘foxy’, then ‘energetic’ will be substituted in; likewise for ‘poodle’ and ‘happy’. If it isn’t either of those values though, then ‘cats win’ will be substituted in.

Regards,
Al.

]]> By: Richard Tallent http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/comment-page-1/#comment-84843 Richard Tallent Thu, 28 Dec 2006 19:08:42 +0000 http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/#comment-84843 In SQL Server, COALESCE() can result in a sub-optimal execution plan, so ISNULL() is better if you only need to test one value for NULL. There are some other differences as well (more info at http://databases.aspfaq.com/database/coalesce-vs-isnull-sql.html) In SQL Server, COALESCE() can result in a sub-optimal execution plan, so ISNULL() is better if you only need to test one value for NULL. There are some other differences as well (more info at http://databases.aspfaq.com/database/coalesce-vs-isnull-sql.html)

]]> By: Jason http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/comment-page-1/#comment-62280 Jason Sun, 05 Nov 2006 01:15:54 +0000 http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/#comment-62280 Good notes. DB2 also uses Coalesce. Good notes. DB2 also uses Coalesce.

]]> By: Raimond Verwei http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/comment-page-1/#comment-14187 Raimond Verwei Wed, 24 May 2006 07:26:53 +0000 http://joseph.randomnetworks.com/archives/2006/03/15/nvl-isnull-ifnull-and-coalesce/#comment-14187 DB2 also supports COALESCE(...) You might want to add that to the list. DB2 also supports COALESCE(…)
You might want to add that to the list.

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