Does Oracle Have a Default DATE Format, and How Should Dates Be Handled Consistently?

Oracle database has no default date format

Unlike most database systems, Oracle Database itself does not specify a fixed format for its DATE data type. This lack of a default format has led to various misunderstandings surrounding the issue.

Detailed explanation of Oracle database date processing

The DATE data type in Oracle Database is internally represented as a 7-byte value containing the year, month, date, hour, minute, and second. When working with dates in an Oracle database, it is important to note the following:

• Dates are not stored as text strings, but as numeric values.
• Oracle uses NLS_DATE_FORMAT to convert between DATE values ​​and string representations based on the user's session settings.
• Each user can customize their own NLS_DATE_FORMAT, causing date strings to be handled differently in different sessions.

Recommended methods to ensure consistency in date processing

To avoid relying on implicit conversions and ensure consistent date processing, it is strongly recommended to use explicit date formats in queries and inserts:

• Use DATE literal: for example, DATE '2018-01-25'
• Use Timestamp literal: for example, TIMESTAMP '2018-01-25 01:23:45'
• Use TO_DATE(date_string, format_string [, nls_values]) to explicitly convert a string to a date: for example, TO_DATE('25-JUN-18', 'DD-MON-RR')

Change default settings

If desired, users can modify their session's NLS_DATE_FORMAT using the command ALTER SESSION SET NLS_DATE_FORMAT = 'desired_format';.

Additional explanation

It is important to emphasize that the NLS_DATE_FORMAT setting only affects how dates are displayed and interpreted when converting between string and DATE values. Regardless of the NLS_DATE_FORMAT setting, the internal representation of DATE is still a 7-byte numeric value.

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