sql - 如何对多个表使用 SQL 连接操作

Question

假设有 7 个这样的表：

class_teacher_lesson

class_teacher_lession_ID, class_ID, teacher_ID, lesson_ID

班级

class_ID, class

老师

teacher_ID, teacher

课

lesson_ID, lesson

学生

student_ID, class_ID, ..., ....

调查回答

survey_answer_ID, survey_question_ID, class_teacher_lession_ID, survey_answer

调查问题

survey_question_ID, survey_question,

结果应该是这样的：

我将通过一个循环得到这个：

数学课：

survey_question (where teacher_id = 11 and lesson_id = 13):
Total Students            Total Students Answered Survey         survey_answer AVG
     155                                45                              79%

survey_question 2 (where teacher_id = 11 and lesson_id = 13):
Total Students            Total Students Answered Survey         survey_answer AVG
     155                                99                              87%

英语课程：

survey_question (where teacher_id = 11 and lesson_id = 15):
Total Students            Total Students Answered Survey         survey_answer AVG
     90                                20                              50%

survey_question 2 (where teacher_id = 11 and lesson_id = 15):
Total Students            Total Students Answered Survey         survey_answer AVG
     90                                25                              34%

到目前为止，我已经尝试过：

SELECT teacher AS 'Teacher', class AS 'Class', lesson AS 'Lesson',
COUNT(student_ID) AS 'Number of students',
COUNT(enquete_antwoord_ID) AS 'Total students answered survey', 
enquete_vraag AS 'Survey Question'
FROM Teacher
LEFT JOIN class_teacher_lesson
ON teacher.teacher_ID = class_teacher_lesson.teacher_ID
LEFT JOIN lesson
ON class_teacher_lesson.class_ID = lesson.lesson_ID
LEFT JOIN class
ON class_teacher_lesson.class_ID = class.class_ID
LEFT JOIN student
ON class.class_ID = student.class_ID
LEFT JOIN survey_answer
ON class_teacher_lesson.class_teacher_lesson_ID = 
survey_answer.class_teacher_lesson
LEFT JOIN survey_question
ON survey_answer.survey_question_ID = survey_question.survey_question_ID
WHERE teacher.teacher_ID = '1158' AND lesson.lesson_ID = '449'
GROUP BY class.class, lesson.lesson, teacher.teacher,
survey_answer.survey_answer, survey_question

有了这个结果：

Teacher:  Class:   Lesson:  Number of students:  Filled in:    Survey_question:
t1        c1       math     54                   54            question1?
t1        c1       math     24                   0             NULL
t1        c1       math     22                   0             NULL

结果应该变成这样：

Teacher:  Class:   Lesson:  Number of students:  Filled in:    Survey_question:
t1        c1       math     90                   54            question1?

score 0 · Accepted Answer

select survey_question, teacher_id, lesson_id , 
       count(1) as Total_student_answer_survey, 
       (select count(1) from student) as total_student,   
       count(1)/(select count(1) from student) * 100 as survey_percentage
from survey_answer sa
inner join survey_question sq 
    on sa.survey_question_id = sq.survey_question_id
inner join class_teacher_lesson ctl 
    on sa.class_teacher_lesson_id = ctl.class_teacher_lesson_id
group by teacher_id, lesson_id, survey_question_id

score 0 · Accepted Answer

我假设enquete_vraag在您的选择中和survey_question在您的问题中实际上是同一列，它只是翻译中遗漏的内容（否则查询将无法选择不在分组依据中的列）。

在这种情况下，您实际上需要做的就是survey_answer.survey_answer从 group by 子句中删除（您也可以将一些左连接更改为内部连接，这可以提高性能。）。

SELECT  teacher AS 'Teacher', 
        class AS 'Class', 
        lesson AS 'Lesson',
        COUNT(student_ID) AS 'Number of students',
        COUNT(enquete_antwoord_ID) AS 'Total students answered survey', 
        enquete_vraag AS 'Survey Question',
        100.0 * COUNT(enquete_antwoord_ID) / COUNT(student_ID) AS 'survey_answer AVG'
FROM    Teacher
        INNER JOIN class_teacher_lesson
            ON teacher.teacher_ID = class_teacher_lesson.teacher_ID
        INNER JOIN lesson
            ON class_teacher_lesson.class_ID = lesson.lesson_ID
        INNER JOIN class
            ON class_teacher_lesson.class_ID = class.class_ID
        LEFT JOIN student
            ON class.class_ID = student.class_ID
        LEFT JOIN survey_answer
            ON class_teacher_lesson.class_teacher_lesson_ID = survey_answer.class_teacher_lesson
        LEFT JOIN survey_question
            ON survey_answer.survey_question_ID = survey_question.survey_question_ID
WHERE   teacher.teacher_ID = '1158' 
AND     lesson.lesson_ID = '449'
GROUP BY class.class, lesson.lesson, teacher.teacher, survey_question

但是（尽管这完全是主观的）我建议使用表别名清理您的查询，并且不要使用单引号来标识列别名（以避免与文字混淆），并且（这更加主观）我已经添加了SQL-Server 特定的Alias = Column_name语法，我个人觉得它更具可读性（Aaron Bertrand 在这里提出了一些更有说服力的切换理由）。

SELECT  t.teacher, 
        c.class, 
        l.lesson,
        [Number of students] = COUNT(s.student_ID),
        [Total students answered survey] = COUNT(sa.enquete_antwoord_ID), 
        [Survey Question] = sq.enquete_vraag,
        [% Students Answered] = 100.0 * COUNT(sa.enquete_antwoord_ID)  / COUNT(s.student_ID)
FROM    Teacher t
        INNER JOIN class_teacher_lesson ctl
            ON t.teacher_ID = ctl.teacher_ID
        INNER JOIN lesson l
            ON ctl.class_ID = l.lesson_ID
        INNER JOIN class c
            ON ctl.class_ID = c.class_ID
        LEFT JOIN student s
            ON c.class_ID = s.class_ID
        LEFT JOIN survey_answer sa
            ON ctl.class_teacher_lesson_ID = sa.class_teacher_lesson
        LEFT JOIN survey_question sq
            ON sa.survey_question_ID = sq.survey_question_ID
WHERE   t.teacher_ID = '1158' 
AND     l.lesson_ID = '449'
GROUP BY c.class, l.lesson, t.teacher, sq.survey_question;

这两种解决方案都应该给出相同的结果，我并不是想把我的偏好强加给任何人，我只是提出选择。这只是一个偏好问题，您会发现哪个更具可读性。

编辑

我认为由于将多个一对多关系连接到同一个“一个”而导致交叉连接，这导致了空调查问题。我认为将聚合移动到子查询可能会有所帮助：

SELECT  t.teacher, 
        c.class, 
        l.lesson,
        [Number of students] = ISNULL(s.Students, 0),
        [Total students answered survey] = ISNULL(sq.Answers, 0), 
        sq.SurveyQuestion,
        [% Students Answered] = 100.0 * ISNULL(sq.Answers, 0) / NULLIF(s.Students, 0)
FROM    Teacher t
        INNER JOIN class_teacher_lesson ctl
            ON t.teacher_ID = ctl.teacher_ID
        INNER JOIN lesson l
            ON ctl.class_ID = l.class_ID
        INNER JOIN class c
            ON ctl.class_ID = c.class_ID
        LEFT JOIN 
        (   SELECT  Class_ID, Students = COUNT(*)
            FROM    student s
            GROUP BY Class_ID
        ) S
            ON c.class_ID = s.class_ID
        LEFT JOIN 
        (   SELECT  sa.class_teacher_lesson_ID, 
                    sq.SurveyQuestion,
                    Answers = COUNT(*)
            FROM    survey_answer sa
                    LEFT JOIN survey_question sq
                        ON sa.survey_question_ID = sq.survey_question_ID
            GROUP BY sa.class_teacher_lesson_ID, sq.SurveyQuestion
        ) sq
            ON ctl.class_teacher_lesson_ID = sq.class_teacher_lesson_ID
WHERE   t.teacher_ID = '1158' 
AND     l.lesson_ID = '449';

sql - 如何对多个表使用 SQL 连接操作

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