<p>Example:</p>

<pre><code>select ename from emp where hiredate = todate('01/05/81','dd/mm/yy')
</code></pre>

<p>and </p>

<pre><code>select ename from emp where hiredate = todate('01/05/81','dd/mm/rr')
</code></pre>

<p>return different results</p>

[{'answer_id': 19061, 'author': 'Michael Stum', 'author_id': 91, 'author_profile': 'https://Stackoverflow.com/users/91', 'pm_score': 7, 'selected': True, 'text': '<p><a href="http://oracle.ittoolbox.com/groups/technical-functional/oracle-dev-l/difference-between-yyyy-and-rrrr-format-519525" rel="noreferrer">http://oracle.ittoolbox.com/groups/technical-functional/oracle-dev-l/difference-between-yyyy-and-rrrr-format-519525</a></p>\n\n<blockquote>\n  <p>YY allows you to retrieve just two digits of a year, for example, the 99 in\n  1999. The other digits (19) are automatically assigned to the current\n  century. RR converts two-digit years into four-digit years by rounding.</p>\n  \n  <p>50-99 are stored as 1950-1999, and dates ending in 00-49 are stored as\n  2000-2049. RRRR accepts a four-digit input (although not required), and\n  converts two-digit dates as RR does. YYYY accepts 4-digit inputs butdoesn\'t\n  do any date converting</p>\n</blockquote>\n\n<p>Essentially, your first example will assume that 81 is 2081 whereas the RR one assumes 1981. So the first example should not return any rows as you most likely did not hire any guys after May 1 2081 yet :-)</p>\n'}, {'answer_id': 19062, 'author': 'mauriciopastrana', 'author_id': 547, 'author_profile': 'https://Stackoverflow.com/users/547', 'pm_score': 3, 'selected': False, 'text': '<p>y2k compatibility. rr assumes 01 to be 2001, yy assumes 01 to be 1901</p>\n\n<p>see: <a href="http://www.oradev.com/oracle_date_format.jsp" rel="nofollow noreferrer">http://www.oradev.com/oracle_date_format.jsp</a></p>\n\n<p>edit: damn! <a href="https://stackoverflow.com/users/91/michael-stum">michael "quickfingers" stum</a> <a href="https://stackoverflow.com/questions/19058/what-is-the-difference-between-oracles-yy-and-rr-date-mask#19061">beat me to it</a>!</p>\n\n<p>/mp</p>\n'}, {'answer_id': 19202, 'author': 'mauriciopastrana', 'author_id': 547, 'author_profile': 'https://Stackoverflow.com/users/547', 'pm_score': 3, 'selected': False, 'text': '<p>@<a href="https://stackoverflow.com/questions/19058/what-is-the-difference-between-oracles-yy-and-rr-date-mask#19066">Michael Stum</a></p>\n\n<blockquote>\n  <p>My last Oracle experience is a bit long ago</p>\n</blockquote>\n\n<p>uhm, was it, before 2000? :p</p>\n\n<p>...</p>\n\n<blockquote>\n  <p>Will yy always assume 19xx? </p>\n</blockquote>\n\n<p><a href="http://oracle.ittoolbox.com/groups/technical-functional/oracle-dev-l/difference-between-yyyy-and-rrrr-format-519525#" rel="nofollow noreferrer">according to your source</a>, we get the following scenarios:</p>\n\n<pre><code>USING\nENTERED\nSTORED\nSELECT of date column\n\n\nYY\n22-FEB-01\n22-FEB-1901\n22-FEB-01\n\n\nYYYY\n22-FEB-01\n22-FEB-0001\n22-FEB-0001\n\n\nRR\n22-FEB-01\n22-FEB-2001\n22-FEB-01\n\n\nRRRR\n22-FEB-01\n22-FEB-2001\n22-FEB-2001 \n</code></pre>\n\n<p>/mp</p>\n'}, {'answer_id': 1042506, 'author': 'vivek', 'author_id': 100823, 'author_profile': 'https://Stackoverflow.com/users/100823', 'pm_score': -1, 'selected': False, 'text': '<p>RR stands for after 1990 and yy assumes 90 as 2090....as we are in the current yr,...</p>\n'}, {'answer_id': 5740115, 'author': 'hariharan', 'author_id': 718361, 'author_profile': 'https://Stackoverflow.com/users/718361', 'pm_score': 1, 'selected': False, 'text': '<p>RR displays four digits as 1999 or 2015(if it is &lt;49 then it will consider 20th century)</p>\n'}, {'answer_id': 34434455, 'author': 'Pritam Bhansali', 'author_id': 4585034, 'author_profile': 'https://Stackoverflow.com/users/4585034', 'pm_score': 0, 'selected': False, 'text': '<h1>About RR or RRRR</h1>\n\n<p>When we are inserting the dates with 2 digits years (i.e. 09/oct/15)\nthen Oracle may changes the centuries automatically hence the \nsolution is 4 digit dates. But 4 digit version is introduced in \nsome recent versions, therefore the solutions for this problem \nin earlier versions was <code>RR</code> or <code>RRRR</code>. But note that it only works \nwith the <code>TO_DATE()</code> function but not with the <code>TO_CHAR()</code> function.</p>\n\n<p>Whenever inserts/updates are conducted upon dates we should always clarify current date running in the clock in association with the date translation since Oracle conducts every date translation by contacting the server.</p>\n\n<p>In order to keep the consistencies among the centuries, it is always better to execute the date translation with 4 digit years.</p>\n\n<h1>About YY or YYYY</h1>\n\n<p>It accepts the dates but doesn\'t has functionality to automatically change it.</p>\n\n<p><a href="https://i.stack.imgur.com/zVJ8D.png" rel="nofollow noreferrer">This Image shows behaviour when inserting date with two digit (i.e. \n09/oct/15)</a></p>\n'}]
['https://Stackoverflow.com/questions/19058', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/1782/']