ต้องการรวมค่าข้อมูลตามช่วงเวลาอ่าครับ ใช้คำสั่ง SQL หรือ php แบบไหนได้บ้างครับ

$con=mysqli_connect("localhost","root","sensorall","sensorroom");
 // Check connect
 if (mysqli_connect_errno()) {
   echo "Failed to connect to MySQL: " . mysqli_connect_error();
 }
if(!empty($_POST['dateStart'])){
	$sql = "SELECT * FROM `power`  where TIME BETWEEN  '".$_POST['dateStart']."' and '".$_POST['dateEnd']."' ORDER BY `time` ";
}else{
	$sql = "SELECT * FROM `power`  where TIME ORDER BY `time` ";
}
	//echo $sql;
 $result = mysqli_query($con,$sql);
 while($row = mysqli_fetch_array($result)) {
  $datax1[] =  $row["time"];
 $datay1[] = $row["mwh"];
//$datay2 [] = $row["lightout"];
// $y2_axis[$i] = $row["lightout"];

 }