https://www.webmaster-forums.net/crss/node/1019579 en https://www.webmaster-forums.net/web-database-development/reliability-rating#comment-1117565 <p><div class="codeblock"><code>SELECT <br />&nbsp;&nbsp;&nbsp; if(PERIOD_DIFF(DATE_FORMAT(NOW(), &#039;%Y%m&#039;), DATE_FORMAT(date_field, &#039;%Y%m&#039;))&gt;24, &#039;30%&#039;,<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if(PERIOD_DIFF(DATE_FORMAT(NOW(), &#039;%Y%m&#039;), DATE_FORMAT(date_field, &#039;%Y%m&#039;))&gt;=12,&#039;50%&#039;,<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if(PERIOD_DIFF(DATE_FORMAT(NOW(), &#039;%Y%m&#039;), DATE_FORMAT(date_field, &#039;%Y%m&#039;))&gt;=6,&#039;80%&#039;,<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if(PERIOD_DIFF(DATE_FORMAT(NOW(), &#039;%Y%m&#039;), DATE_FORMAT(date_field, &#039;%Y%m&#039;))=1,&#039;85%&#039;,&#039;100%&#039;)<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; )<br />&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; )<br />&nbsp;&nbsp;&nbsp; ) as reliability<br />FROM table_name</code></div>'mySQL Docs: <a href="http://www.mysql.com/doc/en/Date_and_time_functions.html" class="bb-url">6.3.4 Date and Time Functions</a></p> <blockquote class="bb-quote-body"><p>Quote:<br /> PERIOD_DIFF(P1,P2) </p> <p>Returns the number of months between periods P1 and P2. P1 and P2 should be in the format YYMM or YYYYMM. Note that the period arguments P1 and P2 are not date values: </p> <p>mysql&gt; SELECT PERIOD_DIFF(9802,199703);<br /> -&gt; 11 </p></blockquote> Mon, 04 Nov 2002 21:42:40 +0000 Mark Hensler comment 1117565 at https://www.webmaster-forums.net