SQL Server JSON output of nested tables - sql

Question

I have the following tables:
create table students
(
id int,
name varchar(10)
)
create table subjects
(
subjectId int,
studentId int,
subject varchar(12)
)
create table marks
(
studentId int,
subjectId int,
marks int
)
create table sports
(
sportId int,
studentId int,
name varchar(12)
)
with the following data:
insert into students values(1, 'Rusty');
insert into subjects values(1, 1, 'math')
insert into subjects values(2, 1, 'science')
insert into marks values(1,1,50)
insert into marks values(1,2,60)
insert into sports values(1, 1, 'soccer')
insert into sports values(2, 1, 'baseball')
I want to write a query in SQL Server to get the following output:
studentId = 1
{
"id": 1,
"name": "Rusty",
"subjects" : [
{
"name": "math",
"marks": 50
},
{
"name": "science",
"marks": 60
}
],
"sports": [
{
"name": "soccer"
},
{
"name": "baseball"
}
]
}
I tried the following query
select *
from students s
join subjects su on (s.id = su.studentId)
join sports sp on (s.id = sp.studentId)
where s.id = 1
for json auto
and here is the output:
[
{
"id": 1,
"name": "Rusty",
"su": [
{
"subjectId": 1,
"studentId": 1,
"subject": "math",
"sp": [
{
"sportId": 1,
"studentId": 1,
"name": "soccer"
}
]
},
{
"subjectId": 1,
"studentId": 1,
"subject": "science",
"sp": [
{
"sportId": 1,
"studentId": 1,
"name": "soccer"
}
]
},
{
"subjectId": 1,
"studentId": 1,
"subject": "math",
"sp": [
{
"sportId": 1,
"studentId": 1,
"name": "baseball"
}
]
},
{
"subjectId": 1,
"studentId": 1,
"subject": "science",
"sp": [
{
"sportId": 1,
"studentId": 1,
"name": "baseball"
}
]
}
]
}
]

Answer 1

For your desired output you can use correlated subqueries for sports and subjects that generate their own JSON, using FOR JSON PATH, and include that information as an array of nested objects in your main JSON output by way of JSON_QUERY (Transact-SQL), e.g.:
/*
* Data setup...
*/
create table students (
id int,
name varchar(10)
);
create table subjects (
subjectId int,
studentId int,
subject varchar(12)
);
create table marks (
studentId int,
subjectId int,
marks int
);
create table sports (
sportId int,
studentId int,
name varchar(12)
);
insert into students (id, name) values
(1, 'Rusty');
insert into subjects (subjectId, studentId, subject) values
(1, 1, 'math'),
(2, 1, 'science');
insert into marks (studentId, subjectId, marks) values
(1,1,50),
(1,2,60);
insert into sports (sportId, studentId, name) values
(1, 1, 'soccer'),
(2, 1, 'baseball');
/*
* Example query...
*/
select
students.id,
students.name,
json_query(( --<<-- doubled brakcets
select
subjects.subject,
marks.marks
from subjects
join marks
on marks.subjectId = subjects.subjectId
and marks.studentId = subjects.studentId
where subjects.studentId = students.id
for json path
)) as [subjects],
json_query(( --<<-- doubled brackets
select
sports.name
from sports
where sports.studentId = students.id
for json path
)) as [sports]
from students
where students.id = 1
for json path, without_array_wrapper;
Which yields the JSON output:
{
"id": 1,
"name": "Rusty",
"subjects": [
{
"subject": "math",
"marks": 50
},
{
"subject": "science",
"marks": 60
}
],
"sports": [
{
"name": "soccer"
},
{
"name": "baseball"
}
]
}