dependent list menu สามารถใช้ค้นหาโดยมีตารางเดียวไหมครับ

<script language = "JavaScript">
//**** List city (Start) ***//
		function Listcity(SelectValue)
		{
			frmMain.ddlcity.length = 0
			frmMain.ddlcertificate.length = 0	
			frmMain.ddlmajor.length = 0	
			//*** Insert null Default Value ***//
			var myOption = new Option('เลือกเมือง','0')  
			frmMain.ddlcity.options[frmMain.ddlcity.length]= myOption
			
			<?
			$intRows = 0;
			$strSQL = "SELECT distinct city,country FROM tb_detail  ORDER BY id ASC ";
			$qr = select($strSQL);
			$intRows = 0;
			while($intRows<count($qr))
			{
			$objResult = $qr[$intRows];
			$intRows++;
			?>			
				x = <?=$intRows;?>;
				mySubList = new Array();
				
				strGroup = <?=$objResult["country"];?>;
				strValue = "<?=$objResult["city"];?>";
				strItem = "<?=$objResult["city"];?>";
				mySubList[x,0] = strItem;
				mySubList[x,1] = strGroup;
				mySubList[x,2] = strValue;
				if (mySubList[x,1] == SelectValue){
					var myOption = new Option(mySubList[x,0], mySubList[x,2])  
					frmMain.ddlcity.options[frmMain.ddlcity.length]= myOption					
				}
			<?
			}
			?>																	
		}
		//**** List city (End) ***//
		
		//**** List certificate (Start) ***//
		function Listcertificate(SelectValue)
		{
			frmMain.ddlcertificate.length = 0	
			frmMain.ddlmajor.length = 0	

			//*** Insert null Default Value ***//
			var myOption = new Option('เลือกใบรับรอง','0')  
			frmMain.ddlcertificate.options[frmMain.ddlcertificate.length]= myOption
			
			<?
			$intRows = 0;
			$strSQL = "SELECT distinct certificate,city FROM tb_detail ORDER BY id ASC ";
			$qr = select($strSQL);
			$intRows = 0;
			while($intRows<count($qr))
			{
			$objResult = $qr[$intRows];
			$intRows++;
			?>
				x = <?=$intRows;?>;
				mySubList = new Array();
				
				strGroup = <?=$objResult["city"];?>;
				strValue = "<?=$objResult["certificate"];?>";
				strItem = "<?=$objResult["certificate"];?>";
				mySubList[x,0] = strItem;
				mySubList[x,1] = strGroup;
				mySubList[x,2] = strValue;
							
				if (mySubList[x,1] == SelectValue){
					var myOption = new Option(mySubList[x,0], mySubList[x,2])  
					frmMain.ddlcertificate.options[frmMain.ddlcertificate.length]= myOption					
				}
			<?
			}
			?>																	
		}
		//**** List certificate (End) ***//
		
		//**** List Major (Start) ***//
		function Listmajor(SelectValue)
		{
			frmMain.ddlmajor.length = 0	

			//*** Insert null Default Value ***//
			var myOption = new Option('เลือกวิชาเอก','0')  
			frmMain.ddlmajor.options[frmMain.ddlmajor.length]= myOption
			
			<?
			$intRows = 0;
			$strSQL = "SELECT distinct major,certificate FROM tb_detail ORDER BY id ASC ";
			$qr = select($strSQL);
			$intRows = 0;
			while($intRows<count($qr))
			{
			$objResult = $qr[$intRows];
			$intRows++;
			?>
				x = <?=$intRows;?>;
				mySubList = new Array();
				
				strGroup = <?=$objResult["certificate"];?>;
				strValue = "<?=$objResult["major"];?>";
				strItem = "<?=$objResult["major"];?>";
				mySubList[x,0] = strItem;
				mySubList[x,1] = strGroup;
				mySubList[x,2] = strValue;
							
				if (mySubList[x,1] == SelectValue){
					var myOption = new Option(mySubList[x,0], mySubList[x,2])  
					frmMain.ddlmajor.options[frmMain.ddlmajor.length]= myOption					
				}
			<?
			}
			?>																	
		}
		//**** List major (End) ***//

</script>


<form  name="frmMain" method="post" action="">
          <label for="Country "></label>
          <table width="100%" border="0" cellspacing="0" cellpadding="0">
            <tr>
              <td align="left">
              <select name="ddlcountry" id="ddlcountry" onChange ="Listcity(this.value);">
              <option selected="selected" value="0">เลือกประเทศ</option>
                <?php
				$sql = "select distinct country from tb_detail order by country asc";
				$qr = select($sql);
				$i=0;
				while($i<count($qr)){
					$rs = $qr[$i];
				$i++;
				?>
				<option value="<?=$rs['country'];?>"><?=$rs["country"];?></option>
				<?php
                }
				?>
              </select>
              </td>
              <td align="center"></td>
              <td align="center">
              <select name="ddlcity" id="ddlcity" onChange ="Listcertificate(this.value)">
              <option selected="selected" value="0">เลือกเมือง</option>
              </select></td>
              <td align="center">&nbsp;</td>
              <td align="center">
              <select name="ddlcertificate" id="ddlcertificate"onChange ="Listmajor(this.value)">
              <option selected="selected" value="0">เลือกใบรับรอง</option>
              </select></td>
              <td align="center">&nbsp;</td>
              <td align="center">
              <select name="ddlmajor " id="ddlmajor ">
              <option selected="selected" value="0">เลือกวิชาเอก</option>
              </select></td>
              <td align="center">&nbsp;</td>
              <td align="center"><input name="textfield" type="text" id="textfield" value="Keyword" /></td>
              <td align="center">&nbsp;</td>
              <td align="right"><input type="submit" name="Search" id="Search" value="Start Search" /></td>
            </tr>
      </table>
        </form>

strGroup = "<?=$objResult["city"];?>";