RE: [PHP-DB] MySQL Conditional Trigger

Dee,

If all you're trying to code is that a value of NULL equates to FALSE
and a date value (whatever date value) equates to true, you can use
something like this:

If ($MyVariable) {
	//... true path blah...
} else {
	//... false path blah...
}

You can use this because NULL equates to false. If you prefer something
more concise, try the following:

$MyVariable ? //True : //False

I'm not a PHP guy so take this with a grain of salt. If I'm full of it,
don't hesitate to correct me.

A-

-----Original Message-----
From: OKi98 [mailto:[email protected]] 
Sent: Monday, December 08, 2008 4:33 PM
To: Dee Ayy
Cc: [email protected]
Subject: Re: [PHP-DB] MySQL Conditional Trigger

-------- Original Message  --------
Subject: [PHP-DB] MySQL Conditional Trigger
From: Dee Ayy <[email protected]>
To: [email protected]
Date: 31.10.2008 17:09
> I don't think my trigger likes a comparison with a variable which is
> NULL.  The docs seem to have a few interesting variations on playing
> with NULL and I was hoping someone would just throw me a fish so I
> don't have to try every permutation (possibly using CASE, IFNULL,
> etc.).
>
> If my ShipDate (which is a date datatype which can be NULL) changes to
> a non-null value, I want my IF statement to evaluate to TRUE.
> IF NULL changes to aDate : TRUE
> IF aDate changes to aDifferentDate : TRUE
> IF anyDate changes to NULL : FALSE
>
> In my trigger I have:
> ...
> IF OLD.ShipDate != NEW.ShipDate AND NEW.ShipDate IS NOT NULL THEN
> ...
>
> Which only works when ShipDate was not NULL to begin with.
> I suppose it evaluates the following to FALSE
> IF NULL != '2008-10-31' AND '2008-10-31' IS NOT NULL THEN
> (not liking the "NULL != '2008-10-31'" part)
>
> Please give me the correct syntax.
> TIA
>
>   
anything compared to NULL is always false
NULL = NULL (NULL included) =>  false
NULL != anything (NULL included) => false
that's why IS NULL exists

I would go this way:

IF NVL(OLD.ShipDate, -1) != NVL(NEW.ShipDate, -1) THEN




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