所以我有以下这些表让我有点头疼。我想要做的是创建一个查询，返回给定类(class)的所有作业，并带有作业信息(成绩、平均成绩等)，或者如果学生没有上交或没有上交作业，则在这些字段中返回空值.我试过 left join但我无法弄清楚这些表。它们很旧而且结构很差，但这就是我所拥有的。
CourseInst_Students 在类(class)实例中为学生保留注册
| ID_CourseInst| SSN |
| =============|=====================|
| 24744 | 080590-XXXX | my ssn
作业_CourseInst 将作业注册到类(class)实例
| ID_Assignment| ID_CourseInst |
| =============|=====================|
| 37978 | 24744 |
| 37979 | 24744 |
| 37992 | 24744 |
| 38046 | 24744 |
作业
| ID_Assignment| Title |
| =============|===========================|
| 37978 | Og þá var kátt í höllinni |
| 37979 | Test for Assignments |
| 37992 | Test 2 |
| 38046 | Eitthvað gott verkefni |
作业_解决方案 保存一组学生(一对多)的信息(成绩、提交日期等)。如果学生没有提交他们的解决方案，则没有记录。
| ID_Assignment| ID_Group | Grade |
| =============|===========================|=========|
| 37978 | 808046 | 10 | only one group has handed in.
作业_解决方案_组将学生的 SSN 注册到一个组。
| ID_Group | SSN |
| =============|===========================|
| 808046 | 221180-XXXX | not my SSN (see mine above)
在为我的 SSN 搜索作业时，我的首选结果如下:
| ID_Assignment| Title | Grade |
| =============|===========================|=========|
| 37978 | Og þá var kátt í höllinni | NULL |
| 37979 | Test for Assignments | NULL |
| 37992 | Test 2 | NULL |
| 38046 | Eitthvað gott verkefni | NULL |
有人能弄清楚吗？谢谢!
更新
这是我到目前为止所得到的
select A.ID_Assignment, A.Title, ASo.Grade
from CourseInst_Students as CS
join Assignments_CourseInst as AC on CS.ID_CourseInst= AC.ID_CourseInst
join Assignments as A on AC.ID_Assignment = A.ID_Assignment
left join Assignments_Solutions as ASo on A.ID_Assignment = ASo.ID_Assignment
left join Assignments_Solutions_Groups as ASGs on ASo.ID_Group = ASGs.ID_Group
where CS.SSN = '080590-XXXX'
AND CS.id_namskeid = 24744
我得到以下结果:
| ID_Assignment| Title | Grade |
| =============|===========================|=========|
| 37978 | Og þá var kátt í höllinni | 10 | <- this is someone else's handin. I want NULL here
| 37979 | Test for Assignments | NULL |
| 37992 | Test 2 | NULL |
| 38046 | Eitthvað gott verkefni | NULL |
最佳答案
假设它是 Oracle，问题出在设计上(绝对是垃圾)。未注册的学生不能提交。在您的情况下，学生 1 已注册，但学生 2 已提交。您最终将使用笛卡尔积来实现所需的结果。请设计这个的人阅读 SQL 的基础知识。
WITH C_S
AS (SELECT
'24744' AS ID_COURSEINST,
'080590-XXXX' AS SSN
FROM
DUAL
UNION ALL
SELECT
'24744' AS ID_COURSEINST,
'221180-XXXX' AS SSN
FROM
DUAL),
A_C
AS (SELECT
'37978' AS ID_ASSIGNMENT,
'24744' AS ID_COURSEINST
FROM
DUAL
UNION ALL
SELECT
'37979' AS ID_ASSIGNMENT,
'24744' AS ID_COURSEINST
FROM
DUAL
UNION ALL
SELECT
'37992' AS ID_ASSIGNMENT,
'24744' AS ID_COURSEINST
FROM
DUAL
UNION ALL
SELECT
'38046' AS ID_ASSIGNMENT,
'24744' AS ID_COURSEINST
FROM
DUAL),
ASSI
AS (SELECT
'37978' AS ID_ASSIGNMENT,
'Og þá var kátt í höllinni' AS TITLE
FROM
DUAL
UNION ALL
SELECT
'37979' AS ID_ASSIGNMENT,
'Test for Assignments' AS TITLE
FROM
DUAL
UNION ALL
SELECT
'37992' AS ID_ASSIGNMENT,
'Test 2' AS TITLE
FROM
DUAL
UNION ALL
SELECT
'38046' AS ID_ASSIGNMENT,
'Eitthvað gott verkefni' AS TITLE
FROM
DUAL),
A_S
AS (SELECT
'37978' AS ID_ASSIGNMENT,
'808046' AS ID_GROUP,
'10' AS GRADE
FROM
DUAL),
A_S_G
AS (SELECT
'808046' AS ID_GROUP,
'221180-XXXX' AS SSN
FROM
DUAL),
GRP_SUBMIT
AS (SELECT
A_S.ID_ASSIGNMENT ID_ASSIGNMENT_AS,
A_S.ID_GROUP ID_GROUP_AS,
A_S.GRADE,
C_S.ID_COURSEINST COURSE_SUB,
C_S.SSN SUBMIT_SSN
FROM
C_S,
A_S,
A_S_G
WHERE
A_S_G.SSN = C_S.SSN
AND A_S_G.ID_GROUP = A_S.ID_GROUP),
GRP_ASSIGN
AS (SELECT
A_C.ID_ASSIGNMENT ID_ASSIGNMENT_AC,
A_C.ID_COURSEINST AS ID_COURSEINST_AC,
ASSI.ID_ASSIGNMENT ID_ASSIGNMENT_ASSI,
ASSI.TITLE TITLE_ASSI,
C_S.ID_COURSEINST COURSE_ASSI,
C_S.SSN ASSI_SSN
FROM
A_C,
ASSI,
C_S
WHERE
A_C.ID_ASSIGNMENT = ASSI.ID_ASSIGNMENT)
SELECT
ID_ASSIGNMENT_ASSI,
TITLE_ASSI,
GRADE
FROM
(SELECT
*
FROM
GRP_SUBMIT
RIGHT OUTER JOIN
GRP_ASSIGN
ON ID_ASSIGNMENT_AS = ID_ASSIGNMENT_AC
AND SUBMIT_SSN = ASSI_SSN)
WHERE
ASSI_SSN = '221180-XXXX'
AND COURSE_ASSI = 24744
ORDER BY
ID_ASSIGNMENT_ASSI;
在 GRP_SUBMIT 中，我检查提交作业的学生数量。
在 GRP_ASSIGN 中，我操纵笛卡尔积的预期提交数量。
在最后的选择中，我让 GRP_SUBMIT 在子查询内的 GRP_ASSIGN 上有一个正确的外部联接，然后根据您的搜索进行过滤。
结果:
输入:221180-XXXX
ID_ASSIGNMENT_ASSI TITLE_ASSI GRADE
------------------ ------------------------- -----
37978 Og þá var kátt í höllinni 10
37979 Test for Assignments
37992 Test 2
38046 Eitthvað gott verkefni
4 rows selected.
输入:080590-XXXX
ID_ASSIGNMENT_ASSI TITLE_ASSI GRADE
------------------ ------------------------- -----
37978 Og þá var kátt í höllinni
37979 Test for Assignments
37992 Test 2
38046 Eitthvað gott verkefni
4 rows selected.
关于sql - 用可能不存在的记录连接表，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19826752/