RE: [PHP-DB] MySQL Conditional Trigger

All,

Chris makes a good point i.e., "unknown compared to anything is
unknown". His comment made me want to clarify my earlier note. In my
earlier example, I wasn't suggesting that-that logic be coded in the
database. I was assuming it would be in the page:

<?php

$TestNullValue = NULL;

If ($TestNullValue) {
	print "Evaluates to true!";
} else {
	print "Evaluates to false!";
}

?>

I tested this, and it worked. Here is why, PHP (like pretty much every
other language) silently casts a NULL to false: 

"When converting to boolean, the following values are considered FALSE:

 - the boolean FALSE itself 
 - the integer 0 (zero) 
 - the float 0.0 (zero) 
 - the empty string, and the string "0" 
 - an array with zero elements 
 - an object with zero member variables (PHP 4 only)
 - the special type NULL (including unset variables)" ("Booleans",
php.net, 05 Dec. 2008).

If you were going to code it in the database, I'd suggest something like
this:

--Using T-SQL here...
DECLARE @TestNullValue SMALLDATETIME

SET @TestNullValue = NULL

If (@TestNullValue Is Null) 
 PRINT 'Evaluates to true!';
ELSE
 PRINT 'Evaluates to false!';

In either case, this should have the same net result.

Be Well,
A-

-----Original Message-----
From: Chris [mailto:[email protected]] 
Sent: Monday, December 08, 2008 5:10 PM
To: OKi98
Cc: [email protected]
Subject: Re: [PHP-DB] MySQL Conditional Trigger


> anything compared to NULL is always false

Actually it's null.

mysql> select false = null;
+--------------+
| false = null |
+--------------+
|         NULL |
+--------------+
1 row in set (0.01 sec)

mysql> select 1 = null;
+----------+
| 1 = null |
+----------+
|     NULL |
+----------+
1 row in set (0.00 sec)

mysql> select 2 = null;
+----------+
| 2 = null |
+----------+
|     NULL |
+----------+
1 row in set (0.00 sec)


unknown compared to anything is unknown.

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