为何修改信息后数据库表中内容为空

//######################学生信息修改1##########################

  include "config.php";

  include "header.php";

?> 




   extract($_REQUEST); 

   $query="update $student_table set name='$name1' where xuehao='$xuehao'";

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query="update $student_table set sex='$sex1' where xuehao='$xuehao'";

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query=mysql_query("update $student_table set class='$class1' where xuehao='$xuehao'");

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query=mysql_query("update $student_table set password='$password2' where xuehao='$xuehao'");

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query=mysql_query("update $student_table set password1='$password3' where xuehao='$xuehao'");

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query); 

   $query="update $student_table set love='$love1' where xuehao='$xuehao'";

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query="update $student_table set telephone='$telephone1' where xuehao='$xuehao'";

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   $query="update $student_table set reward='$reward1' where xuehao='$xuehao'";

   mysql_query("set names 'GB2312'");

   $result=mysql_query($query);

   

   if($password2!=$password3)

 {

     echo"
输入的密码不一致，请重新输入。
";

	 echo "";

	 exit;

 }

			

		if($result==true)

				{

				   echo"
修改信息成功！";

				   echo "";

				   exit;

				 }

				 else

				 {

				   echo"
修改出错，请返回重新修改。
";

				   echo ""; 

				   exit;

				 }

		



?>