To NULL or NOT to NULL that is the question.

January 27, 2012

I liked Shlomi Noach post on “IS TRUE and IS FALSE“.  This kind of logic create bugs.

What will this return?

select if((1 = true) and ( 1 is TRUE) and (NULL is not TRUE), TRUE, FALSE) as answer;

You should know,

NULL is never TRUE or FALSE but

NULL is always NOT TRUE or NOT FALSE.

NULL is a little like a vacuum.  Ancient Greek philosophers did not like to admit the existence of a vacuum, asking themselves “how can ‘nothing’ be something?”.    Does GOD exist in NULL?

If  select “” is NOT NULL; is TRUE what is “”?

select "" is NOT NULL;
+----------------+
| "" is NOT NULL |
+----------------+
|              1 |
+----------------+

Is the lack of an answer, an answer? Is the lack of datum, DATA?  Or should it be “”.  Should we record the blank spaces?

Given:

Create Table
CREATE TABLE `test` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`date` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
`data` varchar(16) DEFAULT NULL,
KEY `id` (`id`)
) ENGINE=MyISAM

When should this happen?

for x = 1 to X;
INSERT INTO `test`(`data`) VALUES ( NULL);
next x;

Null happens.

posted in Commentary by mark

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