Is there Date expressions or function? I'd like to calculate a duration between a date field and today ? Is there a now(), today() function? i'd like this kind of math expression: now() - [field_arrival]
If you only want to display the duration between the given date and today in a view then you don't need any calculation.
Just use time ago display option and display your given date with this time ago option.
You will have the result something like this -- 1 year 3 months ago.
You can drop text ago if you don't need.
Check out time() function. It returns current unix timestamp. Difference of these two fields will give you the difference in seconds which you can convert to minutes/hours/days as needed.
$now = time(); // If $field_arrival is not a Unix timestamp you can use strtotime() to convert it to UNIX timestamp first. $diff = $now - $field_arrival;
Check out the Date Module. It has a sub module called Date Views which gives you what you want: http://drupal.org/project/date.
The generated sql isn't pretty though. If you can use
hook_views_query_alter instead you really should since you have better control over the result sql.
I managed to do this by setting the output format in my source field to timestamp, via custom date format string:
U then in the expression field I used:
time(0) - [field_fieldname]
Now you can see the offset in seconds from now and the field's timestamp, you can convert that into whatever you need with maths, ie:
(time(0) - [field_fieldname]) / ( 60 * 60 )
(time(0) - [field_fieldname]) / ( 60 * 60 * 24)
Turns out the ctools module expects maths functions to always take parameters, the correlated php function is
time(void); so no matter what you put in there it will simply return the current timestamp. Hence the time(0).