Select from three tables with same ID - mysql

Question

I've three tables
students_first_semester_mark (StudentdID,Subject, Semester_I_Mark )
students_second_semester_mark (StudentdID,Subject, Semester_II_Mark )
students_third_semester_mark (StudentdID,Subject, Semester_III_Mark )
I want to have the following kind of output:
_________________________________________________________________________________
|StudentdID | Subject | Semester_I_Mark| Semester_II_Mark | Semester_III_Mark
_________________________________________________________________________________
Please note that Semester_I_Mark or Semester_II_Mark may have Null values.
I'm eager for your answers.

Answer 1

Is this what you want?
SELECT [students_first_semester_mark].[StudentdID]
,[students_first_semester_mark].[Subject]
,[students_first_semester_mark].[Semester_I_Mark]
,[students_second_semester_mark].[Semester_II_Mark]
,[students_third_semester_mark].[Semester_III_Mark]
FROM [students_first_semester_mark]
JOIN [students_second_semester_mark] ON [students_second_semester_mark].[StudentdID] = [students_first_semester_mark].[StudentdID]
JOIN [students_third_semester_mark] ON [students_third_semester_mark].[StudentdID] = [students_second_semester_mark].[StudentdID]

Answer 2

Below is the simplest answer that I can think of.
SELECT T1.StudentdID,T1.Subject,T1.Semester_I_Mark,
T2.Semester_II_Mark, T3.Semester_III_Mark
FROM students_first_semester_mark T1, students_second_semester_mark T2,
students_third_semester_mark T3
JOIN T2 ON T1.StudentdID = T2.StudentdID
JOIN T3 ON T1.StudentdID = T3.StudentdID

Answer 3

This might help you:
SELECT table1.StudentdID, table1.Subject,
table1.Semester_I_Mark, table2.Semester_II_Mark,
table3.Semester_III_Mark
FROM students_first_semester_mark table1
INNER JOIN students_second_semester_mark table2
ON table1.StudentdID = table2.StudentdID
INNER JOIN students_third_semester_mark table3
ON table1.StudentdID = table3.StudentdID

Answer 4

I am assuming that all students will not appear in all subjects.
It will be bit tricky to achieve it in MySQL as it doesn't support full outer join.
To derive FULL OUTER JOIN, you need a LEFT JOIN UNION RIGHT JOIN. As in your case, there are 3 tables, you would need to repeat this for first 2 tables and then UNION them. So the query will be pretty complex to look.
DBFiddle Demo
select * from (
select coalesce(fs.studentdid,t.studentdid) as STUDENTDID
,coalesce(fs.subject,t.subject) as subject
,fs.semester_i_mark,fs.semester_ii_mark,t.semester_iii_mark
from
(
select
coalesce(f.studentdid,s.studentdid) as STUDENTDID,
coalesce(f.subject,s.subject) as subject
,f.semester_i_mark,s.semester_ii_mark
from
STUDENTS_FIRST_SEMESTER_MARK f
left join
STUDENTS_SECOND_SEMESTER_MARK s
on f.studentdid=s.studentdid
and f.subject=s.subject
UNION
select
coalesce(f.studentdid,s.studentdid) as STUDENTDID,
coalesce(f.subject,s.subject) as subject
,f.semester_i_mark,s.semester_ii_mark
from
STUDENTS_FIRST_SEMESTER_MARK f
right join
STUDENTS_SECOND_SEMESTER_MARK s
on f.studentdid=s.studentdid
and f.subject=s.subject
) fs
LEFT JOIN
STUDENTS_THIRD_SEMESTER_MARK t
on fs.STUDENTDID=t.studentdid
and fs.subject=t.subject
) u1
UNION
select * from (
select coalesce(fs.studentdid,t.studentdid) as STUDENTDID
,coalesce(fs.subject,t.subject) as subject
,fs.semester_i_mark,fs.semester_ii_mark,t.semester_iii_mark
from
(
select
coalesce(f.studentdid,s.studentdid) as STUDENTDID,
coalesce(f.subject,s.subject) as subject
,f.semester_i_mark,s.semester_ii_mark
from
STUDENTS_FIRST_SEMESTER_MARK f
left join
STUDENTS_SECOND_SEMESTER_MARK s
on f.studentdid=s.studentdid
and f.subject=s.subject
UNION
select
coalesce(f.studentdid,s.studentdid) as STUDENTDID,
coalesce(f.subject,s.subject) as subject
,f.semester_i_mark,s.semester_ii_mark
from
STUDENTS_FIRST_SEMESTER_MARK f
right join
STUDENTS_SECOND_SEMESTER_MARK s
on f.studentdid=s.studentdid
and f.subject=s.subject
) fs
RIGHT JOIN
STUDENTS_THIRD_SEMESTER_MARK t
on fs.STUDENTDID=t.studentdid
and fs.subject=t.subject
) u2
Coalesce is used so that any not null values of studentdid and subject are returned as we are using outer join.