Question

SELECT 
    lesson_id_1, 
    lesson_id_2, 
    lesson_id_3, 
    lesson_id_4, 
    lesson_id_5, 
    lesson_id_6, 
    lesson_id_7, 
    lesson_id_8, 
    lesson_id_9, 
    lesson_id_10  
FROM hub_attendance 
WHERE 
    student_id='351' AND 
    course_id = '102' AND 
    (
        lesson_id_1 = 300 OR 
        lesson_id_2 = 300 OR 
        lesson_id_3 = 300 OR 
        lesson_id_4 = 300 OR 
        lesson_id_5 = 300 OR 
        lesson_id_6 = 300 OR 
        lesson_id_7 = 300 OR 
        lesson_id_8 = 300 OR 
        lesson_id_9 = 300 OR 
        lesson_id_10 = 300
    ) 
LIMIT 1

我知道它不漂亮，但这是我的MySQL声明。我试图找到它= 300的lesson_id_xx。我怎样才能磨练它以便它只返回单个lesson_id_xx而不是所有它们？

这就是它现在的回报：

array(10) { 
    ["lesson_id_1"]=> string(3) "279" 
    ["lesson_id_2"]=> string(3) "292" 
    ["lesson_id_3"]=> string(3) "293" 
    ["lesson_id_4"]=> string(3) "294" 
    ["lesson_id_5"]=> string(3) "295" 
    ["lesson_id_6"]=> string(3) "296" 
    ["lesson_id_7"]=> string(3) "297" 
    ["lesson_id_8"]=> string(3) "298" 
    ["lesson_id_9"]=> string(3) "299" 
    ["lesson_id_10"]=> string(3) "300" 
}

我只想要这个：

array(10) {
    ["lesson_id_10"]=> string(3) "300" 
}

Answer 1

帮助不大，但您可以使用where缩短in条款：

SELECT
    lesson_id_1, lesson_id_2, lesson_id_3, lesson_id_4, lesson_id_5, 
    lesson_id_6, lesson_id_7, lesson_id_8, lesson_id_9, lesson_id_10  
FROM hub_attendance 
WHERE 
    student_id='351' AND course_id = '102' AND
    300 in (lesson_id_1, lesson_id_2, lesson_id_3, lesson_id_4, lesson_id_5,
            lesson_id_6, lesson_id_7, lesson_id_8, lesson_id_9, lesson_id_10) 
LIMIT 1

但是，我认为真正的答案是，如果你想更容易地查询它，你需要重新设计和规范化这个表。

Answer 2

我认为你在谈论一个桌子（hub_attendance），你有很多lesson_id_xx列代表学生将要学习的课程，即学生可以选择的特定课程有不同的课程选项。这是正确的吗？如果是这样，缩短此陈述的正确方法是根据适当的关系原则重新设计表格，以便有两个表格：

hub_attendance:
id, student_id,  course_id

attendance_lesson:
attendance_id,  lesson_id

此attendance_lesson表是一个表示多对多关系的联接表，即一个课程可以有很多人参加，一个（课程）出勤可以有很多课程。

您的SQL将如下所示（假设您希望课程的所有出席人数均为300）：

SELECT * 
  FROM hub_attendance 
 WHERE EXISTS(SELECT 1 
                FROM attendance_lesson 
               WHERE attendance_lesson.lesson_id = 300 
                 AND attendance_lesson.attendance_id = hub_attendance.id)

Answer 3

我认为你不能做你想做的事情......一旦你在Select中添加了一些内容，就我所知，我无法回复：）

P.S：你应该真正重新设计你的数据库，不要让这个表格像这样......这是冒犯（并且会得罪）很多程序员......

Answer 4

显然应该类似于

SELECT a.*,group_concat(lesson_id) FROM hub_attendance a, hub_lessons l
    WHERE h.id=l.aid AND lesson_id = 300 GROUP BY aid

如何缩短此SQL语句？

4 个答案: