Question

我有一个课程表和课程表，如下所示

course_id  lesson_id content_id seq_no
    1         1          1        1
    1         1          2        2
    1         5          3        1
    1         5          4        2
    1         8          12       1  


leson_id lesson_no course_id

   1        1          1
   5        3          1
   8        2          1

我想在我的应用程序中具有上一个下一个按钮。如果当前课程中有下一课，则单击“ next”；如果当前课程有下一课，则查询应提供下一课目ID；如果没有下一课，则应跳至下一课和第一课。内容的序号为seq_no，课程为lesson_no

我在下面进行了查询，但是我无法跳到下一课

下一次点击：

SELECT * 
FROM course_content
WHERE course_id =1
AND content_id = ( 
SELECT MIN( content_id ) 
FROM course_content
WHERE lesson_id =1
AND content_id >21
ORDER BY seq_no ASC )

以前的点击

SELECT * 
FROM course_content
WHERE course_id =1
AND content_id = ( 
SELECT MAX( content_id ) 
FROM course_content
WHERE lesson_id =1
AND content_id <2
ORDER BY seq_no DESC )

Answer 1

我会这样：

SELECT c.course_id
     , c.lesson_id
     , c.content_id
     , c.seq_no
     , l.lesson_no
  FROM course_content c
  JOIN lesson l 
    ON l.lesson_id = c.lesson_id
 WHERE c.course_id = 1
   AND l.lesson_no     >= :curr_lesson_no
   AND (   c.seq_no     > :curr_seq_no
       OR
           l.lesson_no  > :curr_lesson_no2 
       )
 ORDER
    BY l.lesson_no
       , c.seq_no
   LIMIT 1

只需在查询参数中提供当前行的值lesson_no和seq_no

如果我们无法保留当前行的lesson_no和seq_no，而我们只有content_id，那么我们可以运行查询以获取这些

 SELECT cl.lesson_no   AS curr_lesson_no
      , cc.seq_no      AS curr_seq_no
   FROM course_content cc
   JOIN lesson cl 
     ON cl.lesson_id = cc.lesson_id
  WHERE cc.content_id  = :curr_content_id
  ORDER
     BY cl.lesson_no
      , cc.seq_no
  LIMIT 1

我们可以将这两个查询放在一起……

SELECT c.course_id
     , c.lesson_id
     , c.content_id
     , c.seq_no
     , l.lesson_no
  FROM ( SELECT cl.lesson_no   AS curr_lesson_no
              , cc.seq_no      AS curr_seq_no
           FROM course_content cc
           JOIN lesson cl 
             ON cl.lesson_id = cc.lesson_id
          WHERE cc.content_id  = :curr_content_id
          ORDER
             BY cl.lesson_no
              , cc.seq_no
          LIMIT 1
       ) q
  JOIN lesson l
    ON l.lesson_no   >= q.curr_lesson_no
  JOIN course_content c
    ON c.lesson_id = l.lesson_id
 WHERE c.course_id = 1
   AND (   c.seq_no     > q.curr_seq_no
       OR
           l.lesson_no  > q.curr_lesson_no 
       )
 ORDER
    BY l.lesson_no
       , c.seq_no
   LIMIT 1

如何在MySQL中跳转到下一个ID

1 个答案: