I'm not very attuned to the subtleties of SQL, but this behavior seems
downright strange:
Adding an interval to a timestamp produces the expected result:
cal=> select timestamp without time zone 'jan 1, 1999 00:00:00' + interval '1 month'; ?column?
---------------------1999-02-01 00:00:00
(1 row)
But reversing the two produces nonsense: is this because the values
are implicitly cast to type of the leftmost term in the expression?
cal=> select interval '1 month' + timestamp without time zone 'jan 1, 1999 00:00:00'; ?column?
----------00:00:00
(1 row)
This behavior is perfectly reasonable:
cal=> select timestamp 'jan 1, 1999 00:00:00' + interval '1 month'; ?column?
------------------------1999-02-01 00:00:00-05
(1 row)
And yet, this expression, which just reverse the terms, is downright
weird:
cal=> select interval '1 month' + timestamp 'jan 1, 1999 00:00:00'; ?column?
---------------------1999-01-01 00:00:00
(1 row)
Absolutely nothing happens! It is as if the '1 month' term did not
exist.
Here's the weirdest part:
cal=> select interval '1 month 2:30' + timestamp 'jan 1, 1999 00:00:00'; ?column?
---------------------1999-01-01 02:30:00
(1 row)
It picks up the 2:30, but not the 1 month!
Is this the proper behavior? Or is there likely something wrong,
either with PostgreSQL or my installation of it?
Any comments would be appreciated.
Thanks,
Joe Barillari
