从mysql表中获取值并显示在下拉菜单中选择的值

我正在开发一个非常简单的课程目录。我正在使用动态选择下拉菜单来显示courses特定对象提供的内容academy。最初，我将显示courses available这些选择菜单的完整列表，其中包含名为的mysql数据库表中的值courses_selection_list。然后，我academy_id=15通过标记值来选择提供的课程selected=selected。在Jquery / JS中，您将看到我对文件进行了一次ajax调用，getCourses.php然后在该文件加载页面时显示了选择菜单。

我的问题如下：我只能显示所提供课程的一个价值academy_id=15。如何显示全部？还是有更好的方法呢？演示

courses_offering.php

<script>
    var option = $('#courses_offered').val();
    showFields(option);

    function showFields(option){ 
        var content = '';
        for (var i = 1; i <= option; i++){
            var content = '';
            for (var i = 1; i <= option; i++){
                (function(i) {
                $.ajax({
                        type: "POST",
                    url: "getCourses.php",
                        data: {
                            value: option
                        },
                        success: function (data) {
                            content += '<div id="course_'+i+'">'
                                +'<label>Course # '+i+'</label><br />'
                                +'<label>Course Name:</label>'
                                +'<select id="coursename_'+i+'" name="coursename_'+i+'" class="course_list">'
                                +'<option value="" >--- Select ---</option>"';
                            content += data;
                            content += '</select></div></br>';
                            $('#course_catalog').html(content);
                        }
                    });
                })(i);
            }
            $('#course_catalog').html(content);             
        }
        $('#course_catalog').html(content);
    }
</script>

<select name="courses_offered" id="courses_offered" disabled>
    <?php
    $db_select2  = $db_con->prepare("
        SELECT      academy_id
        FROM        courses_by_academy
        WHERE academy_id = :id
        ");
    if (!$db_select2) return false;
    if (!$db_select2->execute(array(':id' => $id))) return false;
    $courses_count = $db_select2->rowCount();
    echo "<option>----Select----</option>";
    echo "<option value=\"1\"". (($courses_count=="1")?"selected=\"selected\"":"") .">1</option>";
    echo "<option value=\"2\"". (($courses_count=="2")?"selected=\"selected\"":"") .">2</option>";
    echo "<option value=\"3\"". (($courses_count=="3")?"selected=\"selected\"":"") .">3</option>";
    echo "<option value=\"4\"". (($courses_count=="4")?"selected=\"selected\"":"") .">4</option>";
    echo "<option value=\"5\"". (($courses_count=="5")?"selected=\"selected\"":"") .">5</option>";
    ?>
</select>
<div id="course_catalog"></div>  

getCourses.php -课程价值

$id = 15;
//get the course list
$course_query = $db_con->prepare("SELECT course_id, course_name FROM courses_selection_list;");
$course_query->execute();

$data = $course_query->fetchAll();
foreach ($data as $row){
    //select the courses being offered by academy_id=15
    $option = "<option value='".$row["course_id"].":".$row["course_name"]."'";
    $db_select  = $db_con->prepare("
        SELECT academy_id, course_name, course_id, 
               course_start_date, course_end_date
        FROM courses_by_academy
        WHERE academy_id = :id
    ");
    if (!$db_select) return false;
    if (!$db_select->execute(array(':id' => $id))) return false;
    $results = $db_select->fetchAll(\PDO::FETCH_ASSOC);
    if (empty($results)) return false;
    foreach ($results as $value) {
        $result= $value['course_id'];
        if ($result == $row['course_id']) {
            $option .= "selected='selected'";
        }            
    }
    $option .= ">". $row['course_name'] ."</option>";
    //show result
    echo $option;            
}   

Mysql表示例：

courses_selection_list

+-----------+-------------------------+
| course_id |       course_name       |
+-----------+-------------------------+
|         1 | Math                    |
|         2 | English                 |
|         3 | Science                 |
|         4 | Other- Not Listed       |
|         5 | Social Studies          | 
|         6 | Home Mac                |  
|         7 | Business Management     | 
|         8 | Psychology              | 
|         9 | Accounting              | 
|        10 | Advanced Networks       |  
|        11 | Information Techonology |  
+-----------+-------------------------+

courses_by_academy

+----+------------+--------------------------+-----------+------------+----------+
| id | academy_id |  course_name             | course_id | start_date |end_date  |
+----+------------+--------------------------+-----------+------------+----------+
|  1 |         15 | Science                  |         3 |2013-12-04  |2013-12-25|
|  2 |         15 | Business Management      |         7 |2013-12-04  |2013-12-25|
|  3 |         15 | Information Technology   |        11 |2013-12-04  |2013-12-25|
+----+------------+--------------------------+-----------+------------+----------+

所需结果：