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This is my first attempt at creating a website using PHP. My database is done in MySQL. It is for a made up university. I am having trouble creating the page that should allow current students enrolled at the university to search for courses and add them to their schedule. So far, I have the page load up correctly and display the form for the student to enter in the search information. However, whenever a subject is chosen, and the search button clicked, I get an error. I don't know what is causing it so I am not able to finish my page. I'm pretty sure I also have other problems also.

The error message I get is "Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in <file name> on line 210"

I would appreciate it if someone would take the time to look through my code and help me find the problem, and point out any other major problems I might have. If that isn't possible, are there any good tutorials available online that could help me? I've searched google and couldn't find anything useful.

My code is below, I also attached a copy of the .php file

<? //this page allows a user to search for courses being offered.
	require("session.php"); //include the script that handles the session information ?>

<?	$level = $_SESSION["level"];//get the user's level from the session table
	$un = $_SESSION["user"];//get the user's username from the session table
	
/////check to make sure the user is logged in as a student. If not, re-direct them to login page.////////////////////////////	
	if($level != -1)
	{
		print "<script>";
		print " self.location=''";
		print "</script>";
	}
	else
	{
//////connect to the database///////////////////////////////////////////////////////////////////////////////////////////////
    	$usr = "";//database username
    	$pwd = "";//database password
    	$db = "";//database name
    	$host = "localhost";

    	mysql_connect($host,$usr,$pwd);
    	@mysql_select_db ($db) or die( "Unable to select database");?>

<? ///// begin html code to display information on the page///////////////////////////////////////////////////////////////// ?>

		<HTML>
 			<HEAD>
    			<TITLE>Course Search</TITLE>
				<? //include the created template for the layout of the links/header across left and top of page. ?>
				<LINK REL=StyleSheet HREF="template.css" TYPE="text/css">
			</HEAD>
 			<BODY>
 				<div id="mastHead">
    			<?php include("header\University-Header.html"); //include the header at the top of the page.?>
    			</div><? //close mastHead tag
////////////////links that are available from the current page////////////////////////////////////////////////////////////// ?>
				<div id="linkIndex">
	  				<div align="center">
		  				<p><a href="">Login/Logout</a></p>
		  				<p><a href="">View Personal Information</a></p>
		  				<p><a href="">Search for Classes</a></p>
		  				<p><a href="">View Schedule</a></p>
		  				<p><a href="">Pay Bill</a></p>
		  				<p><a href="">View Transcript</a></p>
		  				<p><a href="">View Exam Schedule</a><br><br>
		    			<a href="#"></a><br><br>
		    			<a href="#"></a><br><br><br>
   						</p>
	  				</div><? //close center alignment div tag ?>
 				</div> <? //close linkIndex div tag ?>

    
				<div id="contentsBox"><!--Put all of your code in this div tag.-->
				<div align="center">
				<? 		
					if (isset($_POST['ClassSearch'])) {
						$username="";//database username
						$password="";//database password
						$database="";//database name
						mysql_connect(localhost,$username,$password);
						@mysql_select_db($database) or die( "Unable to select database");	
						
						#set variables
						$Subject= $_POST['Subject'];
						$Section=$_POST['Section'];
						$facid=$_POST['facid'];
						$CourseTitle=$_POST['CourseTitle'];
						$CourseNum=$_POST['CourseNum'];
	
/////statements that check the fields to make sure atleast a subject is entered, and searches according to other criteria.////////
					if($Subject == " ")
					{
						print "<SCRIPT>window.alert('Sorry, you must select a subject.')</SCRIPT>";
						print "<script>";
						print " self.location=''";
						print "</script>"; 
					}//end if
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'";
					}	
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != "") && ($Section != "") && ($facid == "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseNum = '$CourseNum'";
					}	
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'";
					}
	
					// execute mysql statement		   
					$result=mysql_query($query);
					$num=mysql_num_rows($result); 
					mysql_close();

					//check to see if there are no results
					if ($num == 0) 
					{
					echo "<center>I am sorry, but there are no classes being offered that match what you are searching for.
						  <br>Please try searching for something else.</center>";
					}
					
					$i = 0;//initialize i at 0.
					while ($i < $num) 
					{//loops through results until i is no longer less than num.
						$Subject=mysql_result($result,$i,"Subject");
						$Section=mysql_result($result,$i,"Section");
						$facid=mysql_result($result,$i,"facid");
						$CourseTitle=mysql_result($result,$i,"CourseTitle");
						$CourseNum=mysql_result($result,$i,"CourseNum");
						$MeetingTimes=mysql_result($result,$i,"MeetingTImes");
						$Days=mysql_result($result,$i,"Days");
			?>		    
			<!---form to display the class information and allow the student to add it to their schedule if they choose to---> 
							<form id="form1" name="form1" method="post" action="">
  							<table width="336" height="206" border="0" cellpadding="0" cellspacing="0">
    						<tr>
      							<td width="124"><div align="right">Subject:</div></td>
      							<td width="212"><label><?php print $HTTP_GET_VARS['Subject']; ?></label>&nbsp;</td>
    						</tr>
    						<tr>
      							<td><div align="right">Section:</div></td>
      							<td><label><?php print $HTTP_GET_VARS['Section']; ?></label>&nbsp;</td>
    						</tr>
    						<tr>
      							<td><div align="right">Instructor:</div></td>
      							<td><label><?php print $HTTP_GET_VARS['facid']; ?></label>&nbsp;</td>
    						</tr>
    						<tr>
      							<td><div align="right">Course Title: </div></td>
      							<td><label><?php print $HTTP_GET_VARS['Title']; ?></label>&nbsp;</td>
    						</tr>
    						<tr>
      							<td><div align="right">Meeting Times: </div></td>
      							<td><label><?php print $HTTP_GET_VARS['MeetingTimes']; print " "; print $HTTP_GET_VARS['Days']; ?></label>&nbsp;</td>
    						</tr>
    						<tr>
      							<td><div align="right">Course Number: </div></td>
      							<td><label><?php print $HTTP_GET_VARS['CourseNum'];?></label>&nbsp;</td>
    						</tr>
  						</table>
  						<p>
    					<INPUT TYPE="BUTTON" VALUE="Add Class" ONCLICK="window.location.href='<?php echo "$Subject";?>&Section=<?php echo "$Section";?>&facid=<?php echo "$facid";?>&Title=<?php echo "$Title";?>&MeetingTimes=<?php echo "$MeetingTimes";?>&CourseNum=<?php echo "$CourseNum";?>'" />
  						</p>
						</form>;
				<? 	$i++;
					} 
				?> </table></center> <?
				}
				else 
				{?>
			<!------- form to select what information you want to base your search on-------->
  					<form id="form" name="form" method="POST" action="<? $ECHO_SELF?>">
					<p>
          			<label><span class="style2">Search for Courses:</span></label>
          			<br />
        			Use the selection options to search for a course you would like to add to your schedule. 
					You may choose any combination of fields to narrow your  search, but you must select at least one Subject. 
					Click  Search  when your selection is complete.</p>
        			<table width="599" height="226" border="0" cellpadding="0" cellspacing="0">
          				<tr>
            				<td width="119" height="202" valign="top">
								<p><strong>Subject:</strong></p>
              					<p><strong>Course Number:</strong></p>
              					<p><strong>Section:</strong></p>
              					<p><strong>Course Title:</strong></p>
              					<p><strong>Instructor: </strong></p></td>
            				<td width="480" valign="top"><p>
              					<select name="Subject" size="1" id="Subject">
                					<option value=" " selected="selected"></option>
                					<option value="ENGL">ENGL</option>
                					<option value="MATH">MATH</option>
                					<option value="CIS">CIS</option>
                					<option value="PHYS">PHYS</option>
                					<option value="CHEM">CHEM</option>
                					<option value="PEES">PEES</option>
                					<option value="PHIL">PHIL</option>
              					</select>
              			<br />
              			<br />
              					<input name="CourseNum" type="text" id="CourseNum" maxlength="3" />
            					</p>
              					<p>
                				<select name="Section" size="1" id="Section">
                  					<option value=" " selected="selected"> </option>
                  					<option value="1">1</option>
                  					<option value="2">2</option>
                  					<option value="3">3</option>
                  					<option value="4">4</option>
                  					<option value="5">5</option>
                  					<option value="6">6</option>
                  					<option value="7">7</option>
                  					<option value="8">8</option>
                  					<option value="9">9</option>
                  					<option value="10">10</option>
                  					<option value="11">11</option>
                  					<option value="12">12</option>
                  					<option value="13">13</option>
                  					<option value="14">14</option>
                  					<option value="15">15</option>
                  					<option value="16">16</option>
                  					<option value="17">17</option>
                  					<option value="18">18</option>
                  					<option value="19">19</option>
                  					<option value="20">20</option>
                  					<option value="21">21</option>
                  					<option value="22">22</option>
                  					<option value="23">23</option>
                  					<option value="25">25</option>
                				</select>
              					</p>
              					<p>
                				<input name="CourseTitle" type="text" id="CourseTitle" maxlength="25" />
              					</p>
              					<p>
                				<input name="facid" type="text" id="facid" maxlength="15" />
              					</p></td>
          				</tr>
          				<tr>
            				<td height="24" colspan="2" align="left" valign="top"><p>
              					<input name="ClassSearch" type="submit" id="ClassSearch" value="Search" /> 
                   				<input type="reset" name="Reset" value="Reset" />
            					</p>
							</td>
            			</tr>
        			</table>
        			<p>
          			<label></label>
        			</p>
					</form> 
<? 					} 
				}
?></div></div>
			</HTML>
<? //this page allows a user to search for courses being offered.
	require("session.php"); //include the script that handles the session information ?>

<?	$level = $_SESSION["level"];//get the user's level from the session table
	$un = $_SESSION["user"];//get the user's username from the session table
	
/////check to make sure the user is logged in as a student. If not, re-direct them to login page.////////////////////////////	
	if($level != -1)
	{
		print "<script>";
		print " self.location='https://205.153.60.235/login.php?unauth'";
		print "</script>";
	}
	else
	{
//////connect to the database///////////////////////////////////////////////////////////////////////////////////////////////
    	$usr = "";//database username
    	$pwd = "";//database password
    	$db = "";//database name
    	$host = "localhost";

    	mysql_connect($host,$usr,$pwd);
    	@mysql_select_db ($db) or die( "Unable to select database");?>

<? ///// begin html code to display information on the page///////////////////////////////////////////////////////////////// ?>

		<HTML>
 			<HEAD>
    			<TITLE>Course Search</TITLE>
				<? //include the created template for the layout of the links/header across left and top of page. ?>
				<LINK REL=StyleSheet HREF="template.css" TYPE="text/css">
			</HEAD>
 			<BODY>
 				<div id="mastHead">
    			<?php include("header\University-Header.html"); //include the header at the top of the page.?>
    			</div><? //close mastHead tag
////////////////links that are available from the current page////////////////////////////////////////////////////////////// ?>
				<div id="linkIndex">
	  				<div align="center">
		  				<p><a href="https://205.153.60.235/login.php">Login/Logout</a></p>
		  				<p><a href="https://205.153.60.235/ViewCurrentStudentInfo.php">View Personal Information</a></p>
		  				<p><a href="https://205.153.60.235/CourseSearch.php">Search for Classes</a></p>
		  				<p><a href="https://205.153.60.235/ViewClassSchedule.php">View Schedule</a></p>
		  				<p><a href="https://205.153.60.235/ViewTuitionInfo.php">Pay Bill</a></p>
		  				<p><a href="https://205.153.60.235/ViewStudentTranscript.php">View Transcript</a></p>
		  				<p><a href="https://205.153.60.235/ViewExamSchedule.php">View Exam Schedule</a><br><br>
		    			<a href="#"></a><br><br>
		    			<a href="#"></a><br><br><br>
   						</p>
	  				</div><? //close center alignment div tag ?>
 				</div> <? //close linkIndex div tag ?>

    
				<div id="contentsBox"><!--Put all of your code in this div tag.-->
				<div align="center">
				<? 		
					if (isset($_POST['ClassSearch'])) {
						$username="";//database username
						$password="";//database password
						$database="";//database name
						mysql_connect(localhost,$username,$password);
						@mysql_select_db($database) or die( "Unable to select database");	
						
						#set variables
						$Subject= $_POST['Subject'];
						$Section=$_POST['Section'];
						$facid=$_POST['facid'];
						$CourseTitle=$_POST['CourseTitle'];
						$CourseNum=$_POST['CourseNum'];
	
/////statements that check the fields to make sure atleast a subject is entered, and searches according to other criteria.////////
					if($Subject == " ")
					{
						print "<SCRIPT>window.alert('Sorry, you must select a subject.')</SCRIPT>";
						print "<script>";
						print " self.location='https://205.153.60.235/newCourseSearch.php'";
						print "</script>"; 
					}//end if
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND facid LIKE '%$facid'";
					}	
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != "") && ($Section != "") && ($facid == "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'
				   				AND CourseNum = '$CourseNum'";
					}	
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseTitle LIKE '%$CourseTitle'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section != " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND Section = '$Section'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid != "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND facid LIKE '%$facid'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle != "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseTitle LIKE '%$CourseTitle'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum != ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'
				   				AND CourseNum = '$CourseNum'";
					}
					else if (($Subject != " ") && ($Section == " ") && ($facid == "") && ($CourseTitle == "") && ($CourseNum == ""))
					{// setup SQL statement to retrieve the class search results.
	       				$SQL = "SELECT * 
		   		   				FROM university.classes, university.classsections
				   				WHERE Subject = '$Subject'";
					}
	
					// execute mysql statement		   
					$result=mysql_query($query);
					$num=mysql_
  • 4 Contributors
  • 4 Replies
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  • 1 Day Discussion Span
  • Latest Post Latest Post by blackdove

Dani AI

Generated

The immediate cause of the warning is that the result passed to mysql_num_rows is not a valid resource. As noted, the script assigns the SQL text to one variable but calls the query function with a different, undefined variable, so the query fails and mysql_num_rows receives false. Make sure the same variable holds the SQL string every time, that every branch of the big if/else actually sets that SQL string (or build the WHERE clause dynamically), and stop suppressing errors so the real database error becomes visible while debugging.

Several other issues will cause intermittent failures or incorrect results. The code uses short PHP tags (<?) which are often disabled, and it mixes old globals like $HTTP_GET_VARS with POST data — switch to the $_POST/$_GET superglobals. The search form’s action handling is inconsistent (as suggested): posting to the same script should use a valid action or an empty action and correct server variable usage. The SQL combines two tables but never specifies how they link, which produces a Cartesian product; add an explicit JOIN condition. Watch for typos in column names (e.g., mixed capitalization), inconsistent empty-string checks (comparing to a single space), wrong LIKE patterns, and building URLs with unescaped values for the “Add Class” link.

For longer-term stability and security, migrate off the old mysql extension (removed in PHP 7) and use PDO or MySQLi with prepared statements, validate and sanitize inputs on the server, and escape HTML output with htmlspecialchars. Replace the many if/else query branches with a small routine that collects non-empty conditions into an array and joins them with AND. Test iteratively: echo the final SQL, run it in the database client, check the error message from the DB API, then fix the query. See the PHP manual for prepared statements and modern APIs: PDO prepared statements and MySQLi.

Recommended Answers

All 4 Replies

Member Avatar for Johnathan

when i look at your example page in dreamweaver I noticed that on your first form you didnt have an action set this could cause problems I also noticed that dreamweaver doesnt recognize the fact that you have a database set in it you might want to relook your database and make sure that it is set right

Member Avatar for PuneetSeo

plz explain it in short .............

Member Avatar for GliderPilot

Your problem is not with the mysql_num_rows it is with the line before it the mysql_query line.

Your query line looks like this:
$result=mysql_query($query);

However you did not define the $query variable. Technicaly the error is at the query, but because it is not a serious error the code continues to go.

You place your querys in a variable named $SQL

You should replace either the $SQLs with $query or Replace $query with $SQL.

ie.
$result=mysql_query($SQL);

As well as a good habit you should put error catching on your queries to ensure they process properly like so:

$result=mysql_query($SQL) or die("Unable to process database query. Please contact the admin: " . mysql_error());

With this in place if there is an error with the query it will stop processing code, and display the error message above along with the error message from mySql

Member Avatar for blackdove

Thanks, I will try that and see iif I can fix my code from there.

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