Oracle's DATE Data Type: No inherent format
Oracle's DATE
data type stores date and time information internally as a 7-byte value, not a formatted string. This means it lacks a built-in default format.
Source of Misunderstanding
The misconception about a default DATE
format arises when working with text strings. Oracle converts these strings to DATE
objects using the NLS_DATE_FORMAT
session parameter. This parameter's influence creates the impression of a default format.
How Oracle Handles Dates
The actual date handling depends on your Oracle session settings:
-
Text String Input: When inserting a date as a text string without specifying a format, Oracle uses the current
NLS_DATE_FORMAT
setting for conversion. -
Direct
DATE
Input orTO_DATE
: UsingDATE
literals (DATE 'yyyy-mm-dd'
) or theTO_DATE
function with a format mask bypassesNLS_DATE_FORMAT
, ensuring precise conversion.
Best Practices for Date Handling
For clarity and data integrity, always use:
-
DATE
Literals:DATE 'yyyy-mm-dd'
-
TIMESTAMP
Literals:TIMESTAMP 'yyyy-mm-dd HH24:MI:SS'
-
TO_DATE
Function:TO_DATE('date_string', 'format_string')
Specify the format explicitly.
Adjusting NLS_DATE_FORMAT
You can change your session's NLS_DATE_FORMAT
using:
ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';
Default NLS_DATE_FORMAT
Determination
The default NLS_DATE_FORMAT
is determined by the NLS_TERRITORY
session parameter, varying by geographical region. This query shows the format and associated territories:
SELECT f.format, LISTAGG(t.territory, ', ') WITHIN GROUP (ORDER BY t.territory) AS territories FROM (SELECT ROWNUM AS rn, COLUMN_VALUE AS territory FROM TABLE(territories)) t INNER JOIN (SELECT ROWNUM AS rn, COLUMN_VALUE AS format FROM TABLE(formats)) f ON (f.rn = t.rn) GROUP BY f.format;
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