Re: [HACKERS] timestamp subtraction (was Re: formatting intervals with to_char)

On Oct 5, 2006, at 11:50 AM, Tom Lane wrote:
> regression=# select ('2006-09-15 23:59:00'::timestamp - '2006-09-01
> 09:30:41'::timestamp);
>      ?column?
> ------------------
>  14 days 14:28:19
> (1 row)
>
> should be reporting '350:28:19' instead.
>
> This is a hack that was done to minimize the changes in the regression
> test expected outputs when we changed type interval from months/
> seconds
> to months/days/seconds.  But I wonder whether it wasn't a dumb idea.
> It is certainly inconsistent, as noted in the code comments.
>
> I'm tempted to propose that we remove the justify_hours call, and tell
> anyone who really wants the old results to apply justify_hours() to
> the
> subtraction result for themselves.  Not sure what the fallout would
> be,
> though.

I suspect there's applications out there that are relying on that
being nicely formated for display purposes.

I agree it should be removed, but we might need a form of backwards
compatibility for a version or two...

I am personally of the opinion that display logic should never be put into the database.  Applications that rely on the database formatting - that is tightly coupling your application to the database which does not follow good programming principles.

None-the-less, the feature would be nice and may be very valuable for reporting.