Change Oracle's start of week to Sunday

Question

Hi,
I am using Oracle 10g R10.2.0.3.0.
I would like to change the beginning of week in Oracle from Monday to Sunday. Given below is my NLS_DATABASE_PARAMETERS:
NLS_LANGUAGE------------------------AMERICAN
NLS_TERRITORY-----------------------AMERICA
NLS_CURRENCY------------------------$
NLS_ISO_CURRENCY--------------------AMERICA
NLS_NUMERIC_CHARACTE----------------.,
NLS_CHARACTERSET--------------------UTF8
NLS_CALENDAR------------------------GREGORIAN
NLS_DATE_FORMAT---------------------DD-MON-RR
NLS_DATE_LANGUAGE-------------------AMERICAN
NLS_SORT----------------------------BINARY
NLS_TIME_FORMAT---------------------HH.MI.SSXFF AM
NLS_TIMESTAMP_FORMAT----------------DD-MON-RR HH.MI.SSXFF AM
NLS_TIME_TZ_FORMAT------------------HH.MI.SSXFF AM TZR
NLS_TIMESTAMP_TZ_FORMAT-------------DD-MON-RR HH.MI.SSXFF AM TZR
NLS_DUAL_CURRENCY-------------------$
NLS_COMP----------------------------BINARY
NLS_LENGTH_SEMANTICS----------------BYTE
NLS_NCHAR_CONV_EXCP-----------------FALSE
NLS_NCHAR_CHARACTERSET--------------UTF8
NLS_RDBMS_VERSION-------------------10.2.0.3.0
Example of the issue I am trying to resolve:
desc my_table:
EVENT_TIME     TIMESTAMP(6)
query:
SELECT EVENT_TIME, to_char(EVENT_TIME, 'iw') WEEK_NUM
FROM MY_TABLE
returns:
EVENT_TIME               WEEK_NUM
11-NOV-09 09.52.43.000000000 AM     46
10-NOV-09 07.58.32.000000000 AM     46
09-NOV-09 08.49.49.000000000 AM     46
08-NOV-09 10.20.18.000000000 PM     45
07-NOV-09 12.20.38.000000000 AM     45
06-NOV-09 11.55.53.000000000 PM     45
Since 08-NOV-09 10.20.18.000000000 PM, is a Sunday, I would like to see a new WEEK_NUM associated to it. Start of the week should be Sunday 12:00 AM and end of week, Saturday 11:59 PM.
Thank you in advance.
Best,
Anil.
Edited by: user10766354 on Nov 11, 2009 10:22 AM

Answer 1

Hi, Anil,
ISO weeks always begin on Monday, regardless of NLS settings. You can't change that.
You can equate Sundays with the following ISO week by adding 1 to all dates
SELECT EVENT_TIME, to_char(EVENT_TIME + 1, 'iw') WEEK_NUMwhich may be good enough for your purposes.
What are your purposes? What do you need to do?
If you need to group Sunday-through-Saturday weeks, then
TRUNC (event_time, 'd')will use the week depending on NLS_TERRITORY. For America, that means weeks start on Sunday, and the expression above will always be midnight on some Sunday.
Regardless of NLS settings,
TRUNC (event_time + 1, 'iw') - 1is the last Sunday on or before event_time.