Oracle SQL to get first day of month
<p>Requirement is input date should produce first day of the month.
Condtions are:</p>

<ol>
<li>If the date entered is between 16-nov to 30-nov, then the first day will be 16-nov.</li>
<li>if the date entered is between 1-nov to 15-nov , then the first day will be 01-nov.</li>
<li>for all other month it should return 01st day of corresponding month.</li>
</ol>