Updating mysql table field only when condition is met

Question

I have this query:

UPDATE orders SET tracking = '$trackingnumber', tracking_timestamp = NOW() 
WHERE comment like '%$ordernumber%'

Is it possible to update tracking_timestamp ONLY if the value of the field is 0000-00-00 00:00:00?

Answer 1

You can use CASE

UPDATE orders 
SET tracking = '$trackingnumber',
 tracking_timestamp = CASE 
WHEN tracking_timestamp='0000-00-00 00:00:00' 
THEN NOW() 
ELSE tracking_timestamp
 END
WHERE comment like '%$ordernumber%'

Answer 2

use this query

UPDATE orders 
SET tracking = '$trackingnumber', 
tracking_timestamp = IF (tracking_timestamp='0000-00-00 00:00:00',NOW(),'0000-00-00 00:00:00') 
WHERE COMMENT LIKE '%$ordernumber%'