Thread: DATE_PART() BUG? We have an SQL statement that is giving wrong output.

Peter Kelly (pkelly@ets.net) reports a bug with a severity of 1
The lower the number the more severe it is.

Short Description
DATE_PART() BUG?  We have an SQL statement that is giving wrong output.

Long Description
Here are operational details:

RedHat Linux 7.0:

Linux version 2.2.17-14 (root@porky.devel.redhat.com) (gcc version egcs-2.91.66 19990314/Linux (egcs-1.1.2 release)) #1
MonFeb 5 15:25:12 EST 2001 

PostgreSQL Version info:

postgresql-7.0.2-17
postgresql-server-7.0.2-17
postgresql-devel-7.0.2-17

tbs=# SELECT version();
                           version
-------------------------------------------------------------
 PostgreSQL 7.0.2 on i686-pc-linux-gnu, compiled by gcc 2.96
(1 row)

Server/Memory Info:

Server is a Compaq Proliant 2500, Pentium Pro 200 with 256 MB RAM.

[root@lisa cgi-bin]# cat /proc/meminfo
        total:    used:    free:  shared: buffers:  cached:
Mem:  263831552 151920640 111910912 82890752 47788032 74584064
Swap: 271556608  7589888 263966720
MemTotal:    257648 kB
MemFree:     109288 kB
MemShared:    80948 kB
Buffers:      46668 kB
Cached:       72836 kB
BigTotal:         0 kB
BigFree:          0 kB
SwapTotal:   265192 kB
SwapFree:    257780 kB


Sample Code
Here is an example of the whole statement:

SELECT
    *, Date_Part('Month', CAST ('5/25/2001' AS DATE))
    - Date_Part('Month', purchasedate ) + 1 AS thismonth
FROM customers
WHERE CAST('5/25/2001' AS DATE) - CAST ('12 months' AS INTERVAL) < purchasedate
AND purchasedate <= CAST ('5/25/2001' AS DATE)
AND 25 <= Date_Part('Day', purchasedate)
AND Date_Part('Day', purchasedate) <= 25
AND merchantnumber != 'odc12'
ORDER BY thismonth, id_num

Here is a simple example:

SELECT DATE_PART('DAY', CAST('04/1/2001' AS DATE)) as dayofmonth
 dayofmonth
----------
         31

Why does April 1st display as May 31st?

Here is the table def:

CREATE TABLE "customers" (
        "id_num" int4 DEFAULT nextval('customers_id_num_seq'::text) NOT NULL,
        "merchantnumber" character varying(9),
        "producttype" character varying(7),
        "purchasedate" date,
        "emailaddress" character varying(60),
        "firstname" character varying(25),
        "lastname" character varying(50),
        "customerfullname" character varying(40),
        "salesordernumber" character varying(20),
        "notes" character varying(80)
);



No file was uploaded with this report

> Short Description
> DATE_PART() BUG?  We have an SQL statement that is giving wrong output.
> tbs=# SELECT version();
> -------------------------------------------------------------
>  PostgreSQL 7.0.2 on i686-pc-linux-gnu, compiled by gcc 2.96
> Here is a simple example:
> SELECT DATE_PART('DAY', CAST('04/1/2001' AS DATE)) as dayofmonth
> ----------
>          31
> Why does April 1st display as May 31st?

This is a known "feature" of 7.0.x (and earlier) on daylight savings
time boundaries. You will see the problem go away if you set your time
zone to GMT. Upgrade to 7.1.x.

                    - Thomas