Oracle’s Default DATE Format: What You Need to Know
Oracle’s Default DATE Format Explained
If you are new to Oracle SQL, you may be wondering what the default date format is. While some sources may provide conflicting information about the format, it’s important to note that a DATE in Oracle has no inherent format. Instead, the format is determined by the NLS_DATE_FORMAT session parameter.
Let’s explore this further with some Q&A style explanations:
Q: What is a DATE in Oracle?
A: A DATE in Oracle is stored internally as 7 bytes, representing the year (2 bytes) and the month, day, hour, minute, and second (1 byte each).
Q: What is the NLS_DATE_FORMAT session parameter used for?
A: The NLS_DATE_FORMAT session parameter is used to convert strings to dates and vice versa. When a string is passed as a date to Oracle, it attempts to implicitly convert the string to a date using the NLS_DATE_FORMAT parameter for the user’s session as the format model.
Q: What happens if a string is passed as a date without an explicit format?
A: Oracle will attempt to convert the string to a date using the NLS_DATE_FORMAT session parameter. Although, it’s important to note that each user can set their own NLS parameters in their session, which means that relying on implicit conversion can result in errors if the format model differs from the expected format.
Now let’s look at some code examples to illustrate this further.
Inserting a Date into a Table
When inserting a date into a table, it’s important to specify the format explicitly to avoid any issues with implicit conversion. Here’s an example:
INSERT INTO my_table (date_column) VALUES (TO_DATE(‘2022-05-25’, ‘YYYY-MM-DD’));
In this example, we are inserting a date of May 25, 2022 into the “date_column” column of the “my_table” table. We are using the TO_DATE function to convert the string ‘2022-05-25’ to a date, and we are specifying the format model ‘YYYY-MM-DD’ to ensure that the conversion is performed correctly.
Using Date Literals
An alternative to using the TO_DATE function is to use a date literal. Here’s an example:
INSERT INTO my_table (date_column) VALUES (DATE ‘2022-05-25’);
In this example, we are using the DATE literal to specify the date directly in the query. This approach is useful if you know the date in advance and don’t need to convert it from a string.
Changing the NLS_DATE_FORMAT Parameter
If you want to change the NLS_DATE_FORMAT parameter for your session, you can use the following command:
ALTER SESSION SET NLS_DATE_FORMAT = ‘YYYY-MM-DD’;
This command sets the NLS_DATE_FORMAT parameter to ‘YYYY-MM-DD’, which means that any subsequent conversions from strings to dates will use this format.
In summary, the default date format in Oracle is determined by the NLS_DATE_FORMAT session parameter. While it’s tempting to rely on implicit conversion, it’s safer to specify the format explicitly to avoid any issues with unexpected format models. Using date literals is another option for specifying dates directly in SQL queries, and changing the NLS_DATE_FORMAT parameter can be useful if you want to enforce a specific format for your session.