When I click the submit button from the form without entering any values, it displays the message Please fill all the fields and error for the query. But it also generates the following notice: 
Notice: Undefined variable: sql in C:\XAMPP\htdocs\statistics\savecourseadminscores.php on line 31
Is this normal?
saveITScores.php
 <?php
 define('DB_NAME','some');//false name
 define('DB_USER','some');//false name
 define('DB_PASSWORD','some');//false name
 define('DB_HOST','localhost');
 $connect = mysql_connect(DB_HOST,DB_USER,DB_PASSWORD);
 if(!$connect){
      die('Could not connect:'.mysql_error());
 }
 $db_selected=mysql_select_db(DB_NAME,$connect);
 if(!$db_selected){
   die('Can\'t use'.DB_NAME.':'.mysql_error());
 }
$value1=$_POST['s1'];
$value2=$_POST['s2'];
$value3=$_POST['year'];
if(isset($_POST['submit'])){
    if($value1 && $value2 && $value3){
       $sql="INSERT INTO itservice(s1,s2,year)    VALUES('$value1','$value2','$value3')";
    }
    else{
       echo "Please fill all the fields.";
    }
}
  if(!mysql_query($sql)){
     die('Error:'.mysql_error());
  }
  mysql_close();
  ?>
saveForm.php
  <div id="form">
<form action="saveITScores.php" method="POST">
S1: <input class="inputfield" type="text" name="s1" size="5"> <br /><br/>
S2: <input class="inputfield" type="text" name="s2" size="5"> <br /><br/>
<b>Year:<b/>
<select name="year"> 
<option value="Choose">Please select..</option>
<option value="2005">2005</option> 
<option value="2006">2006</option>
<option value="2007">2007</option>
<option value="2008">2008</option>
<option value="2010">2010</option>
<option value="2011">2011</option>
<option value="2012">2012</option></select><br/><br/>
<br/>
<input type="submit" value="Save" name="submit">
<input type="reset" name="reset" value="Clear"><br /><br/>
 
    