<h3>week() function</h3>
Extract the week number from a date, or the number of weeks
from a <code>Interval</code>

<h4>Syntax</h4>
<code>week(date)</code><br>
<code>week(Interval)</code><br>

<h4>Arguments</h4>
<code>date</code> - is date or datetime. The date to extract the week from.
<br>
<code>Interval</code> - is Interval. The Interval to return the number of weeks from.

<h4>Example</h4>
<!-- Show example of function.-->
<code>week('2012-05-12') &rarr; 19</code><br>
<code>week(tointerval('3 weeks')) &rarr; 3</code><br>
<code>week(age('2012-01-01','2010-01-01')) &rarr; 104.285...</code><br>