PHP在新表单后删除变量

Question

在我的代码中，我有两个表单供用户选择选项。第一个变量将保存，但一旦用户提交第二个表单，第一个表单中的变量将不再保存。

<div class = "school">
<h3>Please select the university you previously attended</h3>
<form action = "" method = "post" name = "school_form">
<select name="school" size ="10">

<?php
//shows options for $selected_school
$sql = "SELECT DISTINCT school FROM data;";
$result = mysqli_query($conn, $sql);
$resultCheck = mysqli_num_rows($result);
if ($resultCheck > 0){
while($row = mysqli_fetch_assoc($result)){
  // inserts all data as array
  echo "<option>". $row['school'] ."</option>";
      }
 }
?>

</select>
<br>
<input type ="submit" name = "submit_school" value = "Enter">
</form>
<?php
//saves selected option as $selected_school
if(isset($_POST['submit_school'])){
$selected_school = mysqli_real_escape_string($conn, $_POST['school']);
echo "You have selected: " .$selected_school;
}
?>

</div>
<div class ="courses">
<h3>Please select the courses you took</h3>
<form action = "" method ="post" name ="course_form">

<?php
//user shown options for courses
$sql2 = "SELECT transfer_course, transfer_title FROM data WHERE school = ? ORDER BY transfer_course ASC";
$stmt = mysqli_stmt_init($conn);
if(!mysqli_stmt_prepare($stmt, $sql2)) {
echo "SQL statement failed";
} else {
mysqli_stmt_bind_param($stmt, "s", $selected_school);
mysqli_stmt_execute($stmt);
$result2 = mysqli_stmt_get_result($stmt);

while($row2 = mysqli_fetch_assoc($result2)){
echo "<input type='checkbox' name ='boxes[]' value = '" . $row2['transfer_course'] . "' >" . $row2['transfer_course'] . "<br>";
      }
 }
?>
<br>
<input type ="submit" name = "submit_courses" value = "Enter">
</form>
<br>
<?php
//saved selected option(s) as $selected_course
if(isset($_POST['submit_courses'])){//to run PHP script on submit
   if(!empty($_POST['boxes'])){
      foreach($_POST['boxes'] as $selected_course){
         echo "You have selected: " . $selected_course . "</br>";
      }
   }
 }
 ?>
 </div>
<div class = "output">
<h3>Course Equivalency</h3>
<?php
$sql3 = "SELECT arcadia_course, arcadia_title FROM data WHERE school = " . $selected_school . " AND transfer_course = " . $selected_course . "";
$result3 = mysqli_query($conn, $sql3);
if($result3)
{
  while($row3 = mysqli_fetch_assoc($result3)){
    echo $row3['arcadia_course'] . " " . $row3['arcadia_title'] . "<br>";
 }
 } else {
    echo "failed";
    echo $sql3;
}

 ?>

所以当我进入下一条 sql 语句时

$sql3 = "SELECT arcadia_course, arcadia_title FROM data WHERE school = " . $selected_school . " AND transfer_course = " . $selected_course . "";

选择学校时会保存变量，但选择课程后$selected_school又变成空白了。

我已经在页面顶部设置了 session_start()。

Answer 1

您可以使用session 变量，这将有助于使数据可以跨各个页面访问。

因此，无论何时提交表单，您都可以在会话中保存该值并随时检索它。在您的 php 文件顶部，您需要启动会话，即session_start();。然后在您的代码中

<?php
//saves selected option as $selected_school
if(isset($_POST['submit_school'])){
 $_SESSION['selected_school ']=$selected_school;// here you are storing value to session 
$selected_school = mysqli_real_escape_string($conn, $_POST['school']);
echo "You have selected: " .$selected_school;
}
?> 

您也可以对$selected_course 执行相同操作。然后您可以将值传递给您的查询，如下所示：

$sql3 = "SELECT arcadia_course, arcadia_title FROM data WHERE school = " .$_SESSION['selected_school ']. " AND transfer_course = " .$_SESSION['selected_course']. "";

更多信息请参考here

Answer 2

您的选项似乎没有传递的值。在你的第一个形式 while 循环中试试这个：

echo '<option value="' . $row['school'] . '">' . $row['school'] . '</option>';

您可能还遇到了更多问题。如果这不能解决您的问题，我会更深入地挖掘。

编辑：然后，是的，正如其他人所建议的那样，您可能还想添加一个隐藏的输入字段以在第二个表单提交上传递该变量值。

我们所说的隐藏输入字段是这样的：

<input type="hidden" name="selected_school" value="<?php if(isset($selected_school) echo $selected_school; ?>">