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From "Bryan Talbot (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HIVE-1253) date_sub() function returns wrong date because of daylight saving time difference
Date Sat, 20 Mar 2010 00:11:27 GMT

     [ https://issues.apache.org/jira/browse/HIVE-1253?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Bryan Talbot updated HIVE-1253:
-------------------------------

    Affects Version/s:     (was: 0.5.0)
                       0.6.0
         Release Note: Fix off-by-one issue with date_sub and date_add when date ranges include
a daylight savings time change.
               Status: Patch Available  (was: Open)

date_sub and date_add used both a Calendar and a SimpleDateFormat object; however, the UTC
timezone was only set for the Calendar object.  This causes the computation to sometimes be
incorrect when the date ranges cross daylight savings time changes.

The patch removes specifying the UTC timezone for the Calendar object so that both Calendar
and the SimpleDateFormat will use the default timezone.  This should allow the date math to
be consistent with other potential date math functions as long as they all use the default
timezone.

If the user wishes to use a specific timezone that is not the system default, it can be set
using the normal java ways (e.g. setting user.timezone, etc.).


> date_sub() function returns wrong date because of daylight saving time difference
> ---------------------------------------------------------------------------------
>
>                 Key: HIVE-1253
>                 URL: https://issues.apache.org/jira/browse/HIVE-1253
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Query Processor
>    Affects Versions: 0.6.0
>            Reporter: mingran wang
>
> date_sub('2010-03-15', 7) returns '2010-03-07'. This is because we have time shifts on
2010-03-14 for daylight saving time.
> Looking at ql/src/java/org/apache/hadoop/hive/ql/udf/UDFDateSub.java, it is getting a
calendar instance in UTC time zone.
> def calendar = Calendar.getInstance(TimeZone.getTimeZone("UTC"));
> And use calendar.add() to substract 7 days, then conver the time to 'yyyy-MM-dd' format.
> If it simply uses default timezone, the problem is solved: "def calendar = Calendar.getInstance());"
> When people use date_sub('2010-03-15', 7), I think they mean substract 7 days, instead
of substracting 7*24 hours. So it should be an easy fix. The same changes should go to date_add
and date_diff

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