php - SQL JOIN 查询不显示任何内容 - PHP

Question

我正在执行一个 sql 查询，但它没有从表中返回任何数据。我不确定为什么，我已经从 INNER 更改为 LEFT 但没有运气。我已多次修改查询，但找不到问题。想知道为什么我没有显示任何内容吗？

TABLE STRUCTURE

TABLE CREATE QUERY

PHP

$query = ("SELECT  class.class_name, class.class_caption, class.class_credit_hours, class.class_description, faculty_fname, faculty_lname
            FROM class
            LEFT JOIN section 
            ON class.id = section.class_id
            LEFT JOIN faculty 
            ON faculty.id = section.faculty_id OR faculty.id = office_hours.faculty_id
            LEFT JOIN faculty_titles
            ON faculty_titles.faculty_id = faculty.id
            LEFT JOIN faculty_education
            ON faculty_education.faculty_id = faculty.id 
            LEFT JOIN major_class_br
            ON major_class_br.class_id = class.id
            LEFT JOIN major_minor 
            ON major_class_br.major_minor_id = major_minor.id
            LEFT JOIN sched_sect_br 
            ON sched_sect_br.section_id =  section.id
            LEFT JOIN schedule
            ON schedule.id = sched_sect_br.schedule_id
            LEFT JOIN semester
            ON semester.id = schedule.semester_id
            LEFT JOIN office_hours
            ON schedule.id = office_hours.schedule_id AND faculty.id = office_hours.faculty_id       
                 ");
      //execute query
      $result = mysql_query($query);

     if ($result){

    $totalhours = 0;

    while ($row = mysql_fetch_assoc( $result ))
    {  
        print "<b>" . $row['class_name'] . "</b><br>";
        print $row['class_caption'] . "<br>";
        print $row ['class_credit_hours'] . "hrs. <br>";
            print $row ['faculty_lname'] . "hrs. <br>";
            print $row ['faculty_fname'] . "hrs. <br>";
        print $row['class_description'] . "<br>";      
        print "------------------------------<br />";
        $totalhours += $row['class_credit_hours']; 
    }   
    }

    print "<p>Total hours for Major: " . $totalhours . ".</p>";

所需的显示:

Computer Programming I
CP1000
4
James Doe
This course offers introduction to programming. 

更新:这里发现了问题，但我不确定原因

ON faculty.id = section.faculty_id OR faculty.id = office_hours.faculty_id

Answer 1

• 复制 SQL，转到 MySQL 管理员，在那里执行 SQL 并查看它是否返回任何结果。

• 删除所有的 JOIN 并再次执行，您至少应该看到一些东西

• 一个一个添加JOIN

• 尝试确定哪个 JOIN 导致没有返回任何行

• 检查连接的左侧和右侧，确保确实有有效数据要连接

或者使用 OUTER JOIN