interval->day first cut

I've completed my first cut of adding a day field to the interval  
struct and patched up the regression tests for places where it failed  
due to the new behavior (e.g., interval '19:00' + interval '6:00' =  
interval '25:00'). I haven't added any regression tests for the DST  
behavior, but it works (and this could be the start of the regression  
tests). Note: DST changed on 2005-04-03:

test=# SET TIME ZONE 'CST7CDT';
SET
test=# SELECT * FROM TIMESTAMPTZ_TBL;           t1
------------------------
2005-03-31 22:00:00-07
2005-04-01 22:00:00-07
2005-04-02 22:00:00-07
2005-04-03 23:00:00-06
(4 rows)

test-#     , t1 + INTERVAL '24 hours' as "+24 hours" FROM  
TIMESTAMPTZ_TBL;           t1           |         +1 day         |       +24 hours
------------------------+------------------------ 
+------------------------
2005-03-31 22:00:00-07 | 2005-04-01 22:00:00-07 | 2005-04-01 22:00:00-07
2005-04-01 22:00:00-07 | 2005-04-02 22:00:00-07 | 2005-04-02 22:00:00-07
2005-04-02 22:00:00-07 | 2005-04-03 22:00:00-06 | 2005-04-03 23:00:00-06
2005-04-03 23:00:00-06 | 2005-04-04 23:00:00-06 | 2005-04-04 23:00:00-06
(4 rows)

test=# SELECT t1, t1 - INTERVAL '1 day' as "-1 day"
test-#     , t1 - INTERVAL '24 hours' as "-24 hours" FROM  
TIMESTAMPTZ_TBL;           t1           |         -1 day         |       -24 hours
------------------------+------------------------ 
+------------------------
2005-03-31 22:00:00-07 | 2005-03-30 22:00:00-07 | 2005-03-30 22:00:00-07
2005-04-01 22:00:00-07 | 2005-03-31 22:00:00-07 | 2005-03-31 22:00:00-07
2005-04-02 22:00:00-07 | 2005-04-01 22:00:00-07 | 2005-04-01 22:00:00-07
2005-04-03 23:00:00-06 | 2005-04-02 23:00:00-07 | 2005-04-02 22:00:00-07
(4 rows)

test=# SELECT INTERVAL '1 day' = INTERVAL '24 hours';
?column?
----------
t
(1 row)

One interesting fallout of this is that adding two SQL-compliant  
intervals can produce non-SQL-compliant output:

test=# select interval '3 days 16:39' + interval '1 day 15:32' as  
"interesting";   interesting
-----------------
4 days 32:11:00
(1 row)

On a related issue, Tom commented:

> The spec says what results you must get from
> spec-compliant input; I don't think it says we may take only
> spec-compliant input.  (If we were to read it that way, we'd have
> to rip out every PG extension, not only the interval-related ones.)
>
> The entire *point* of this change is to be able to distinguish
> "25 hours" from "1 day 1 hour", so you can hardly argue that being
> able to do that is not what we want it to do...

I've added a interval_simplify function which assumes 1 day = 24  
hours and puts the interval in SQL-spec form. This could be exposed  
to let people "reduce" their intervals. However, I'm concerned this  
is surprising behavior.

Thoughts?

Michael Glaesemann
grzm myrealbox com