Question

我有这个有效的SQL查询：

SELECT * from ( SELECT distinct ts.users_user_id
          from subjects s LEFT JOIN teachers_subjects ts
          ON s.subject_ID = ts.subject_id
          JOIN users_teachers ut
          ON ut.user_id = ts.users_user_id
          LEFT JOIN stations st
          ON st.station_id = ut.station_id
          LEFT JOIN majors mj
          ON mj.major_id = ut.major_id
          ".$where." ) qualified
          JOIN users u ON qualified.users_user_id = u.user_id
          JOIN users_teachers ut ON qualified.users_user_id = ut.user_id
          JOIN teachers_subjects ts2 ON qualified.users_user_id = ts2.users_user_id
          JOIN subjects s2 ON ts2.subject_id = s2.subject_id
          LEFT JOIN stations st ON ut.station_id = st.station_id"

这是为了a）能够匹配某些搜索条件和b）允许我为每个结果输出多个subject_id，因为每个结果代表一个教授多个主题的教师，这就是为什么有两个连接相同的栏目。

我现在必须添加另外两个连接来添加这个混乱。

SELECT * from ( SELECT distinct ts.users_user_id
          from subjects s LEFT JOIN teachers_subjects ts
          ON s.subject_ID = ts.subject_id
          JOIN users_teachers ut
          ON ut.user_id = ts.users_user_id
          LEFT JOIN stations st
          ON st.station_id = ut.station_id
          LEFT JOIN majors mj
          ON mj.major_id = ut.major_id

              LEFT JOIN lessons l
              ON l.teacher_id = ut.user_id
              LEFT JOIN ratings r
              ON r.lesson_id = l.lesson_id    

          ".$where." ) qualified
          JOIN users u ON qualified.users_user_id = u.user_id
          JOIN users_teachers ut ON qualified.users_user_id = ut.user_id
          JOIN teachers_subjects ts2 ON qualified.users_user_id = ts2.users_user_id
          JOIN subjects s2 ON ts2.subject_id = s2.subject_id

               LEFT JOIN lessons l2 ON l.teacher_id = qualified.users_user_id
               LEFT JOIN ratings r2 ON r2.lesson_id = l2.lesson_id

          LEFT JOIN stations st ON ut.station_id = st.station_id"

不幸的是，我没有得到所需的输出。 a）没有输出正确的课程ID（只有少数几个应该输出）和b）从课程表派生的数组中的项目数量是它应该的n倍，其中n =数字该老师的科目。所以有很多冗余和很多空数组插槽

非常感谢任何帮助

课程表结构：

    CREATE TABLE `lessons` (
   `lesson_id` int(11) NOT NULL AUTO_INCREMENT,
   `lesson_date` date NOT NULL,
   `time_began` time NOT NULL,
   `time_ended` time NOT NULL,
   `duration` int(11) NOT NULL COMMENT 'minutes',
   `total_fee` int(11) NOT NULL,
   `student_id` int(11) NOT NULL,
   `teacher_id` int(11) NOT NULL,
   `request_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
   `pay_rate` int(11) NOT NULL,
   `subject_id` int(11) NOT NULL,
   `student_reject` tinyint(4) NOT NULL DEFAULT '0',
   `student_reject_comment` text,
   `lesson_notes` text,
   PRIMARY KEY (`lesson_id`),
   KEY `student_id` (`student_id`),
   KEY `teacher_id` (`teacher_id`)
 ) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=40 ;

评级表结构：

CREATE TABLE `ratings` (
`lesson_id` int(11) NOT NULL,
`like_dislike` tinyint(4) NOT NULL,
`review` text NOT NULL,
PRIMARY KEY (`lesson_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

期望的输出：

[rej] => Array
    (
        [avatar] => 122.JPG
        [email] => 
        [last_name] => kob
        [user_name] => rej1324558654
        [english_name] => Array
            (
                [0] => SAT                    
                [1] => math
            )

        [station_en_name] =>
        [country_prefix] => AR
        [pay] => 201
        [lesson_id] => Array
            (
                [0] => 11
                [1] => 12
                [2] => 13
                [3] => 14
            )

    )

原始输出具有每个主题名称的四倍，而不是正确的课程ID，而不是在lesson_id数组中有许多空白插槽

Answer 1

这可能不是你想听到的，但我真的强烈建议将这个查询分成多个一口大小，可测试的块。它会添加一些I / O，但您可以使用VIEWS或CTE控制它，具体取决于您的环境。虽然它可能不适合生产运行，但拥有控制总数可以让您首先确定问题的来源。

如果您决定这样做，我将从以下

开始

SELECT COUNT(DISTINCT subject_ID) FROM subjects; 
SELECT COUNT(DISTINCT subject_id) FROM teachers_subjects;
SELECT count(*)
   FROM  subjects as s
   INNER JOIN teachers_subjects as ts
      ON s.subject_ID = ts.subject_id ;

然后向下移动列表并测试所有连接。

测试所有这些工作需要付出很多努力，但无论是在修复现在的问题还是解决以后可能遇到的任何问题，它都可能会得到回报。如果这是一个实时数据环境，你可以合理地预期最终会出现问题...某些数据加载不正确或者其他什么。预先编写控制总数将允许您稍后放大以解决可能出现的任何问题，而不仅仅是您正在开始的那个问题

具有多个连接的SQL查询，我正在添加更多

1 个答案: