What is the difference between 'YYYY' and 'RRRR' in Oracle SQL

Question

I have 2 queries in SQL:

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

and

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

Both are giving me the same result. What is the difference between 'RRRR' and 'YYYY'?

Answer 1

YYYY gives the current year as 4 digits.

RRRR format means 2-digit years in the range 00 to 49 are assumed to be in the current century (ie have the same first two digits as the current year), and years given as 50 through 99 are assumed to be in the previous century.