SQL查询选择每名学生使用子查询无法使用从父查询行使用出勤

Question

我有一个问题在SQL中，我试图找出学生出席在一个注册系统中的类我正在建设但它赢了“别让我在子查询中使用父列，

SELECT A.student_id, TRUNCATE((100 - ((100/B.reg_num) * C.abs_num)), 0) AS attendance FROM 
students A 
JOIN (
SELECT COUNT(*) AS reg_num 
FROM students 
JOIN seminargroup_student ON seminargroup_student.student_id = students.student_id 
JOIN seminar_group ON seminar_group.seminar_group_id = seminargroup_student.seminar_group_id 
JOIN modules ON modules.module_id = seminar_group.seminar_group_module_id 
JOIN register_seminar ON register_seminar.seminar_id = seminar_group.seminar_group_id 
JOIN registers ON registers.register_id = register_seminar.register_id 
WHERE modules.module_id =1 AND students.student_id = A.student_id 
) B 
JOIN (
SELECT COUNT(*) AS abs_num 
FROM students 
JOIN seminargroup_student ON seminargroup_student.student_id = students.student_id 
JOIN seminar_group ON seminar_group.seminar_group_id = seminargroup_student.seminar_group_id 
JOIN modules ON modules.module_id = seminar_group.seminar_group_module_id 
JOIN absence ON students.student_id = absence.student_id 
WHERE modules.module_id =1 AND students.student_id = A.student_id 
) C 

这将返回：＃1054 - 未知列‘A.student_id’在‘where子句’

感谢您的帮助！

Answer 1

尝试重写你的查询：

SELECT students.student_id, TRUNCATE((100 - ((100/B.reg_num) * C.abs_num)), 0) AS attendance FROM 
students 
JOIN ( 
SELECT COUNT(*) AS reg_num 
FROM students A 
JOIN seminargroup_student ON seminargroup_student.student_id = A.student_id 
JOIN seminar_group ON seminar_group.seminar_group_id = seminargroup_student.seminar_group_id 
JOIN modules ON modules.module_id = seminar_group.seminar_group_module_id 
JOIN register_seminar ON register_seminar.seminar_id = seminar_group.seminar_group_id 
JOIN registers ON registers.register_id = register_seminar.register_id 
HAVING modules.module_id =1 AND students.student_id = A.student_id 
) B 
JOIN ( 
SELECT COUNT(*) AS abs_num 
FROM students A 
JOIN seminargroup_student ON seminargroup_student.student_id = A.student_id 
JOIN seminar_group ON seminar_group.seminar_group_id = seminargroup_student.seminar_group_id 
JOIN modules ON modules.module_id = seminar_group.seminar_group_module_id 
JOIN absence ON A.student_id = absence.student_id 
HAVING modules.module_id =1 AND students.student_id = A.student_id 
) C 

UPD：WHERE子句替换为具有和别名移动的子查询中。 由于在SELECT之前计算WHERE，可能会导致错误。

而且这些问题可以帮助你解决这个问题：
2. WHERE vs HAVING

Answer 2

它不会让我在子查询中使用父列

一般来说，您不需要在FROM中的子查询中引用父代。

相反，你只需要添加您的加盟领域的SELECT和GROUP BY子句中的子查询，然后加入

例如

SELECT students.student_id, 
     Truncate((100 - ((100/b.reg_num) * c.abs_num)), 0) AS attendance 
FROM students 
     JOIN (SELECT a.studentid, 
        Count(*) AS reg_num 
      FROM students A 
        JOIN seminargroup_student 
         ON seminargroup_student.student_id = A.student_id 
        JOIN seminar_group 
         ON seminar_group.seminar_group_id = 
         seminargroup_student.seminar_group_id 
        JOIN modules 
         ON modules.module_id = 
         seminar_group.seminar_group_module_id 
        JOIN register_seminar 
         ON register_seminar.seminar_id = 
         seminar_group.seminar_group_id 
        JOIN registers 
         ON registers.register_id = register_seminar.register_id 
      GROUP BY a.studentid) A 
     ON students.studentid = a.student.id 
     JOIN (SELECT a.studentid, 
        Count(*) AS abs_num 
      FROM students aA 
        JOIN seminargroup_student 
         ON seminargroup_student.student_id = a.student_id 
        JOIN seminar_group 
         ON seminar_group.seminar_group_id = 
         seminargroup_student.seminar_group_id 
        JOIN modules 
         ON modules.module_id = 
         seminar_group.seminar_group_module_id 
        JOIN absence 
         ON a.student_id = absence.student_id 
      GROUP BY a.studentid) b 
     ON students.studentid = b.student.id 

作为一个侧面说明，你不必做两子查询，如果您使用的是左联接和做一个重复计数的PK区域，而不是对*

SELECT 
    A.student_id, 
    TRUNCATE((100 - ((100/counts.reg_num) * counts.abs_num)), 0) AS attendance 
FROM 
students A 
JOIN 
(SELECT 
    COUNT(DISTINCT absence.absence_id) AS abs_num , --OR whatever the PK is 
    COUNT(DISTINCT registers.regeister_id) as reg_num, 
    students.student_id 


FROM students 
     JOIN seminargroup_student 
     ON seminargroup_student.student_id = students.student_id 
     JOIN seminar_group 
     ON seminar_group.seminar_group_id = 
      seminargroup_student.seminar_group_id 
     JOIN modules 
     ON modules.module_id = seminar_group.seminar_group_module_id 

     LEFT JOIN register_seminar 
     ON register_seminar.seminar_id = seminar_group.seminar_group_id 
     LEFT JOIN registers 
     ON registers.register_id = register_seminar.register_id 


     LEFT JOIN absence 
     ON students.student_id = absence.student_id 
GROUP BY 
    students.student_id) COUNTS 
ON a.student_id = coutnts.student_ID