รบกวนอีกทีนะครับ ค่า sum ไม่ sum ติดเงื่อนไขอะไรหรือเปล่า ครับ

<style type="text/css"> 
@media print 
{ 
#non-printable { display: none; } 
#printable { display: block; } 
} 
</style>
<div id="non-printable">
<center><table width="744" border="0">
<tr>
<td width="62" height="73">&nbsp;</td>
<td width="10">&nbsp;</td>
<td width="29">&nbsp;</td>
<td width="539">
<?php
ini_set('display_errors', 1);
error_reporting(~0);

$strKeyword = null;

if(isset($_POST["txtKeyword"]))
{
$strKeyword = isset($_POST['txtKeyword']) ? $_POST['txtKeyword'] : null;
}

?>
<?php
ini_set('display_errors', 2);
error_reporting(~0);

$strKeyword1 = null;

if(isset($_POST["txtKeyword1"]))
{
$strKeyword1 = isset($_POST['txtKeyword1']) ? $_POST['txtKeyword1'] : null;
}

?>

<form name="frmSearch" method="post" action="<?php echo $_SERVER['SCRIPT_NAME'];?>">
<table width="502" border="1">
<tr>
<th width="492"><center>
  เดือน
<input name="txtKeyword" type="text" id="txtKeyword" size="20" value="<?php echo $strKeyword;?>">
  ปี
  <input name="txtKeyword1" type="text" id="txtKeyword1" size="20" value="<?php echo $strKeyword1;?>">
<input type="submit" value="ค้นหา"></th>
</tr>
</table>
</form>
</td>
<td width="82">&nbsp;</td>
</tr>
</table></center>
</div>
<div id="printable">
<table width="747" border="0" align="center">
  <tr>
    <td width="741"><center>รายงานสรุปการลา/หยุดของ พนักงาน </center></td>
  </tr>
  <tr>
    <td><center>หจก.อึ้งเจริญพูลทรัพย์ลำนารายณ์ </center></td>
  </tr>
  <tr>
    <td><center>193 หมู่ที่ 1 ต.ชัยนารายณ์ อ.ชัยบาดาล จ.ลพบุรี 15130</center></td>
  </tr>
  <tr>
    <td><center>เบอร์โทรศัพท์ 081-8649127 , 036-461258 , 632258</center></td>
  </tr>
  <tr>
    <td><center><div id="non-printable"><input type="button" value="พิมพ์เอกสาร" onClick="window.print()"></div></center></td>
  </tr>
</table>
<form>
<?php

$serverName = "localhost";
$userName = "root";
$userPassword = "";
$dbName = "project";

$conn = mysqli_connect($serverName,$userName,$userPassword,$dbName);
//$sql = "select sum(lk_number) as lk_number from lack group by per_id ,lk_month ,lk_year ";
//$sql = "select * FROM lack WHERE lk_month LIKE '%".$strKeyword."%' AND lk_year LIKE '%".$strKeyword1."%' ";

$sql = "select per_id,per_name,lk_month,lk_year, ";
$sql .= "lk_cause,lk_cause1,sum(lk_number)  as lk_number ";
$sql .= " FROM lack WHERE lk_month LIKE '%".$strKeyword."%' AND lk_year LIKE '%".$strKeyword1."%'  ";
$sql .= " group by per_id,per_name,lk_month,lk_year,lk_cause,lk_cause1 ";
$query = mysqli_query($conn,$sql);

?>
<table width="831" border="1" align="center">
<tr>
<th width="96"> <div align="center">รหัสพนง.</div></th>
<th width="139"> <div align="center">ชื่อ-นามสกุล</div></th>
<th width="112"> <div align="center">วันเดือนปี</div></th>
<th width="85"> <div align="center">สาเหตุ</div></th>
<th width="96"> <div align="center">อื่นๆ</div></th>
<th width="104"> <div align="center">สถิตการหยุด</div></th>
<th width="153">เซ็นรับทราบ</th>
</tr>

<?php
while($result=mysqli_fetch_array($query,MYSQLI_ASSOC))
{
?>
<tr>
<td><div align="center"><?php echo $result["per_id"];?></div></td>
<td><div align="center"><?php echo $result["per_name"];?></div></td>
<td><div align="center"><?php echo $result["lk_month"];?>-<?php echo $result["lk_year"];?></div></td>
<td align="right"><?php echo $result["lk_cause"];?></td>
<td align="right"><?php echo $result["lk_cause1"];?></td>
<td align="right"><?php echo $result["lk_number"];?></td>
<td width="153"></td>
</tr>
<?php
}
?>
</table>
<p>
<?php
mysqli_close($conn);
?>
</div>

$conn = mysqli_connect($serverName,$userName,$userPassword,$dbName);
$sql = "select sum(lk_number) as lk_number from lack group by per_id ,lk_month ,lk_year ";
$sql = "select * FROM lack WHERE lk_month LIKE '%".$strKeyword."%' AND lk_year LIKE '%".$strKeyword1."%' ";

$query = mysqli_query($conn,$sql);

$sql = "select * FROM lack WHERE lk_month LIKE '%".$strKeyword."%' AND lk_year LIKE '%".$strKeyword1."%' ";

$sql = "select sum(lk_number) as lk_number from lack group by per_id ,lk_month ,lk_year ";