ขอสอบถามหน่อยครับเรื่องการกำหนดช่วงเดือน/ปี sql...

<?php
function lastDate($date='', $format='Y-m-d')
{
	$rs = strtotime('-6 month', strtotime(date('Y-m-d')));
	if ($date <> '') 
	{
		$rs = strtotime('-6 month', strtotime($date));
	}
	return date($format, $rs);
}
echo lastDate();
echo '<br/>';
echo lastDate('2016-01-02');
?>

<?php
function lastDate($last_month='-6 month', $date='', $format='Y-m-d')
{
	$rs = strtotime($last_month, strtotime(date('Y-m-d')));
	if ($date <> '') 
	{
		$rs = strtotime($last_month, strtotime($date));
	}
	return date($format, $rs);
}
echo lastDate('+3 month');
echo '<br/>';
echo lastDate('-2 week');
echo '<br/>';
echo lastDate('-2 day', '2016-01-02');
?>

<?php
function lastDate($last_month='-6 month', $date='', $format='Y-m-d')
{
	$rs = strtotime($last_month, strtotime(date('Y-m-d')));
	if ($date <> '') 
	{
		$rs = strtotime($last_month, strtotime($date));
	}
	return date($format, $rs);
}
$strsql = "SELECT * FROM table WHERE fieldDate BETWEEN '".lastDate("-3 month")."' AND DATE_FORMAT(now(),'%Y-%m-%d')");//fieldDate: date format: yyyy-mm-dd
//หรือ
$strsql = "SELECT * FROM table WHERE fieldDate >= '".lastDate("-6 month")."'";