php - 未定義のインデックス [php]

Question

検索用にこのコードを取得しましたが、問題が発生しています。うまく機能しますが、検索タブをクリックするとエラーが表示されます。しかし、検索用のクエリを入力してみると、問題なく動作します。

エラーは次のとおりです。

Notice: Undefined index: searching in F:\Programs\wamp\www\a\search.php on line 45
Notice: Undefined index: find in F:\Programs\wamp\www\a\search.php on line 46
Notice: Undefined index: field in F:\Programs\wamp\www\a\search.php on line 47

コードは次のとおりです。

<h2>Search</h2> 
 <form name="search" method="post" action="search.php">
 Seach for: <input type="text" name="find" /> in 
 <Select NAME="field">
 <Option VALUE="firstname">First Name</option>
 <Option VALUE="lastname">Last Name</option>
 <Option VALUE="location">Location</option>
 </Select>
 <input type="hidden" name="searching" value="yes" />
 <input type="submit" name="search" value="Search" />
 </form>


 <?php 


 $searching = $_POST['searching'];
 $find = $_POST['find'];
 $field = $_POST['field'];

 //This is only displayed if they have submitted the form 

 if ($searching =="yes") 
 { 
 echo "<h2>Results</h2><p>"; 

 //If they did not enter a search term we give them an error 
 if ($find == "") 
 { 
 echo "<p>You forgot to enter a search term"; 
 exit; 
 } 

 // Otherwise we connect to our Database 
 mysql_connect("localhost", "root", "root") or die(mysql_error()); 
 mysql_select_db("chess") or die(mysql_error()); 

 // We preform a bit of filtering 
 $find = strtoupper($find); 
 $find = strip_tags($find); 
 $find = trim ($find); 

 //Now we search for our search term, in the field the user specified 
 $data = mysql_query("SELECT * FROM members WHERE upper($field) LIKE'%$find%'"); 

 echo "<table border=1>";
echo "<tr><td>Codename</td><td>Location</td><td>Rating</td></tr>";



 //And we display the results 
 while($result = mysql_fetch_array( $data )) 
 { 
 echo $result['firstname']; 
 echo " "; 
 echo $result['lastname']; 
 echo "<br>"; 
 echo $result['location']; 
 echo "<br>"; 
 echo "<br>"; 
 } 

 //This counts the number or results - and if there wasn't any it gives them a little message explaining that 
 $anymatches=mysql_num_rows($data); 
 if ($anymatches == 0) 
 { 
 echo "Sorry, but we can not find an entry to match your query<br><br>"; 
 } 

 //And we remind them what they searched for 
 echo "<b>Searched For:</b> " .$find; 
 } 



 ?>