What is the Default DATE Format in Oracle and Why is it Misunderstood?

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 or TO_DATE: Using DATE literals (DATE 'yyyy-mm-dd') or the TO_DATE function with a format mask bypasses NLS_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:

<code class="language-sql">ALTER SESSION SET NLS_DATE_FORMAT = 'YYYY-MM-DD HH24:MI:SS';</code>

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:

<code class="language-sql">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;</code>

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