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