YYYY vs. RRRR in Oracle TO_DATE: What's the Difference?

Understanding the Nuances of 'YYYY' and 'RRRR' in Oracle SQL

In Oracle SQL, the use of 'YYYY' and 'RRRR' as format masks in the TO_DATE function can lead to confusion due to their similarities. While both masks result in four-digit years, there are subtle differences between them.

Truncation Format: 'YYYY'

The 'YYYY' format mask represents the year in four digits based on the current system date. For example:

select trunc(to_date('27-Jul-1987'),'YYYY') FROM dual;

Output:

1987

Two-Digit Year Assumption: 'RRRR'

The 'RRRR' format mask uses a different approach. It interprets years represented as two digits as follows:

• Years in the range 00 to 49 are assumed to be in the same century as the current year.
• Years in the range 50 through 99 are assumed to be in the previous century.

Consider the following example:

select trunc(to_date('27-Jul-1987'),'RRRR') FROM dual;

Output:

1987

In this case, since the year '87' falls within the range 50 through 99, it is interpreted as 1987 based on the 'previous century' assumption.

Implications for Data Manipulation

Understanding the difference between 'YYYY' and 'RRRR' is crucial when dealing with dates, especially when working with two-digit years. For example, if you need to compare dates across multiple centuries, using 'YYYY' ensures accuracy, while 'RRRR' may lead to incorrect results if two-digit years are present.

In conclusion, 'YYYY' provides the exact four-digit year based on the current system date, while 'RRRR' employs assumptions based on the two-digit year input. The choice between 'YYYY' and 'RRRR' depends on the specific requirements and the presence of two-digit years in your data.

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