Nested Array in JSON - JOIN using JSON_TABLE - oracle12c

Question

Using Oracle 12c, I have a JSON structure as below:
{
"class": {
"students": [{
"name": "Joe",
"rollnum": 11,
"homephone": 3211113312,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 53
}, {
"subject_id": 23,
"marks": 43
}, {
"subject_id": 24,
"marks": 35
}, {
"subject_id": 25,
"marks": 90
}, {
"subject_id": 26,
"marks": 87
}]
}, {
"name": "Toe",
"rollnum": 12,
"homephone": 1231231122,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 66
}, {
"subject_id": 23,
"marks": 77
}, {
"subject_id": 24,
"marks": 88
}, {
"subject_id": 25,
"marks": 90
}, {
"subject_id": 26,
"marks": 98
}]
},
{
"name": "Roe",
"rollnum": 15,
"homephone": 3332221111,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 56
}, {
"subject_id": 23,
"marks": 57
}, {
"subject_id": 24,
"marks": 87
}, {
"subject_id": 25,
"marks": 66
}, {
"subject_id": 26,
"marks": 76
}]
}
]
}
}
A class has multiple students and each student is enrolled to multiple subjects. This data is being stored as a JSON LOB structure in a table column. Now, when I try to join the SubjectID from the nested array to the Subject master table, it does not work. However, if I try to query for a particular subject (or others); it works perfectly fine.
Below is the query, I am using. Please help.
SELECT sjson.name,sjson.rollnum,sm.subject_name,sjson.marks
FROM
students s,
JSON_TABLE(ss.student_json,'$.class.students[*]'
columns(
name varchar2(50) path '$.name',
rollnum number path '$.rollnum',
homephone number path '$.homephone',
joined_on varchar2 path '$.joined_on' ,
nested path '$.subjects[*]' columns(
subject_id number path '$.subject_id',
marks number path '$.marks'
)
)
)sjson,
subject_master sm
WHERE sjson.name = 'Joe'
AND sjson.subject_id = sm.subject_id;

Answer 1

1) table 'students' is aliases as 's' but the JSON_TABLE input refers to 'ss'. I assume this is just a type.
2) you do not explain what 'does not work' mean? Are you seeing no rows returned or an error message?
3) i tries your query (with minor changes) on 12.1.0.2 RELEASE and it appears to work:
create table subject_master (id number, name varchar2(20));
insert into subject_master values(21, 'a');
insert into subject_master values(23, 'b');
insert into subject_master values(24, 'c');
insert into subject_master values(25, 'd');
insert into subject_master values(26, 'e');
create table students (student_json clob);
insert into students values ('{
"class": {
"students": [{
"name": "Joe",
"rollnum": 11,
"homephone": 3211113312,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 53
}, {
"subject_id": 23,
"marks": 43
}, {
"subject_id": 24,
"marks": 35
}, {
"subject_id": 25,
"marks": 90
}, {
"subject_id": 26,
"marks": 87
}]
}, {
"name": "Toe",
"rollnum": 12,
"homephone": 1231231122,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 66
}, {
"subject_id": 23,
"marks": 77
}, {
"subject_id": 24,
"marks": 88
}, {
"subject_id": 25,
"marks": 90
}, {
"subject_id": 26,
"marks": 98
}]
},
{
"name": "Roe",
"rollnum": 15,
"homephone": 3332221111,
"joined_on": "2016-03-01",
"subjects": [{
"subject_id": 21,
"marks": 56
}, {
"subject_id": 23,
"marks": 57
}, {
"subject_id": 24,
"marks": 87
}, {
"subject_id": 25,
"marks": 66
}, {
"subject_id": 26,
"marks": 76
}]
}
]
}
}');
SELECT sjson.name,sjson.rollnum,sm.name,sjson.marks
FROM
students s,
JSON_TABLE(s.student_json,'$.class.students[*]'
columns(
name varchar2(50) path '$.name',
rollnum number path '$.rollnum',
homephone number path '$.homephone',
joined_on varchar2 path '$.joined_on' ,
nested path '$.subjects[*]' columns(
subject_id number path '$.subject_id',
marks number path '$.marks'
)
)
)sjson,
subject_master sm
WHERE sjson.name = 'Joe'
AND sjson.subject_id = sm.id;
NAME ROLLNUM
-------------------------------------------------- ----------
NAME MARKS
-------------------- ----------
Joe 11
a 53
Joe 11
b 43
...