MYSQL comma separated result with two types

Question

I have 4 tables, as below.

Table: Class

ClassID     |   ClassSTD
--------------------------------
1           |   STD-1
2           |   STD-2
3           |   STD-3
4           |   STD-4

Table: Section

SectionId   |   SectionName | ClassId
--------------------------------------------
1           |   sec-A       | 1
2           |   sec-B       | 1
3           |   sec-C       | 1
4           |   sec-A       | 2
5           |   sec-B       | 2
6           |   sec-C       | 2
7           |   sec-A       | 3

Table: Subject

subjectId   |   subjectName
------------------------------------
1           |   Art
2           |   Music
3           |   Play

Table SubjectAllocationToClass

classId     |   sectionID           |   subjectId   | type
-----------------------------------------------------------------------
1(STD-1)        |   1(sec-A)            |   1(Art)      | main
1(STD-1)        |   2(sec-B)            |   1(Art)      | main
1(STD-1)        |   3(sec-C)            |   1(Art)      | optional
1(STD-1)        |   1(sec-A)            |   2(Music)    | main
1(STD-1)        |   2(sec-B)            |   2(Music)    | optional

Above table "SubjectAllocationToClass" shows distribution of two type of subject (Main and optional) to section for class.

Need All Class irrespective of section or subjectAllocation Need All Section irrespective of subjectAllocation

How I can achieve below result from SELECT statement?

    classSTD |  sectionName | Main subjectName   | Optional subjectName
    -----------------------------------------------------------------------------
    STD-1    |  sec-A       | Art, Music         |
    STD-1    |  sec-B       | Art                |  Music
    STD-1    |  sec-C       |                    |  Art
    STD-3    |  sec-A       |                    |
    STD-4    |              |                    |

Answer 1

You can use GROUP_CONCAT() along with CASE expression to have a conditional grouping like below

select c.ClassID, s.sectionName,
xx.`Main subjectName`,
xx.`optional subjectName`
from Class c
join Section ss on c.ClassID  = ss.ClassID     
join (
select sa.sectionID,
group_concat(case when sa.type = 'main' then s.subjectName else null end) as  `Main subjectName`,
group_concat(case when sa.type = 'optional' then s.subjectName else null end) as  `optional subjectName`
from SubjectAllocationToClass sa
join Subject s on sa.subjectId = s.subjectId   
group by sa.subjectId ) xx on ss.SectionId = xx.SectionId;

Answer 2

select 
  ClassSTD as ClassSTD, 
  sectionname AS SectionName, 
  COALESCE(GROUP_CONCAT(CASE WHEN sac.type = 'main' THEN subjectName END), '')  as 'Main subjectname',
  COALESCE(GROUP_CONCAT(CASE WHEN sac.type = 'optional' THEN subjectName END), '')  as 'Optional subjectname'
FROM SubjectAllocationToClass sac
JOIN  Class c  ON c.classid = sac.classid
JOIN Section sc ON sc.sectionid = sac.sectionid
JOIN Subject sj ON  sj.subjectid = sac.subjectid
GROUP BY ClassSTD, SectionName;