下拉菜单php与下一个/上一个按钮

我有:

<select name="department" id="department" onchange="this.form.submit()">
    <?php 
        do { 
    ?>
        <option value="<?php echo $row_department['dept_Name'] ?>"><?php echo $row_department['dept_Name'] == $department ? 'selected' : ''?><?php echo $row_department['dept_Name'] 
        ?></option>
    <?php
    } while ($row_department = mysql_fetch_assoc($department));
    $rows = mysql_num_rows($department);
    if($rows > 0) {
      mysql_data_seek($department, 0);
	  $row_department = mysql_fetch_assoc($department);
    } 
    ?>
</select>

对于数据库名称为department的下拉列表。

一旦下拉选择，多个文件集将从数据库中查看，如id, name, dept_name与下一个/上一个按钮。

问题是，每当我点击下一个/上一个按钮，没有文件查看。

必须第二次选择下拉菜单以查看第二个文件集。

我该怎么做?我用的是Dreamweaver CS6

 $deptName = $row['dept_Name'];
 $sql = mysql_query("SELECT * FROM (table_name) WHERE (column_department_name) = '$deptName'");
  while ($row_department = mysql_fetch_assoc($sql));
   $rows = mysql_num_rows($row_department);
  if($rows > 0) {
     echo $rows['(your_column_name)'];
  }else{
      echo 'nothing';
  }