From: | Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> |
---|---|
To: | PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org> |
Subject: | Strange results with date/interval arithmetic |
Date: | 2002-01-08 19:10:50 |
Message-ID: | 200201081910.g08JAoJ13410@candle.pha.pa.us |
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Lists: | pgsql-hackers |
I am seeing strange results from date/interval computations involving
months.
I get the correct answers because I have a negative setting relative to
GMT. Here are my results with TZ=EST5EDT:
test=> select '2001/3/1'::date - '1 month'::interval;
?column?
------------------------
2001-02-01 00:00:00-05
(1 row)
With GMT it is OK too:
test=> select '2001/3/1'::date - '1 month'::interval;
?column?
------------------------
2001-02-01 00:00:00+00
(1 row)
However, with GMT+1 I see a big failure:
test=> select '2001/3/1'::date - '1 month'::interval;
?column?
------------------------
2001-01-29 00:00:00+01
(1 row)
Why does it say 2001-01-29?
This is interesting:
test=> select '2001/7/1'::date - '1 month'::interval;
?column?
------------------------
2001-05-31 00:00:00+02
(1 row)
test=> select '2001/8/1'::date - '1 month'::interval;
?column?
------------------------
2001-07-01 00:00:00+02
(1 row)
Because August and July have the same number of months, it worked. I am
going to research this but someone may know the solution already.
--
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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