在 PHP 中执行查询的问题

我在以下代码中遇到问题，如何管理 sql 字符串，因为它无法检索字符串中的问题问题如何更正字符串

    <?php
                       $chapter = $_SESSION['chapters'] ;
                   if(isset($chapter)) 
                      {
                         $nchapter = count($chapter );
                        echo("You selected $nchapter chapters:<br> ");
                    for($i=0; $i < $nchapter; $i++)
                       {
                         ($chapter[$i] . " ,");
                             echo  $var1 = $chapter[$i] . " <br>";
                          $_SESSION['var1'] = $var1;
                        $db = mysql_connect("127.0.0.1","root","");
                        $db_select = mysql_select_db("db",$db);
                      echo  $var1 ;
                     echo $sql = "select * from ".$_SESSION['tcsub']." where                                       chapter='$var1'";
      $query = mysql_query($sql) or die(mysql_error());
     while($row=mysql_fetch_array($query))
      {
             echo  $data= htmlspecialchars_decode($row['question'], ENT_QUOTES);
          }
     }
  } 
?>