OpenJson in SQL Server for nested json data? - json

Question

I have a json data like this:
[
{"id": 1}, {"id": 3}, {"id": 2, "children": [{"id": 4}, {"id": 5}]}
]
Please help me how to parse this data into relational data:
Column: Id Order/Index ParentId
---------------------------------------
1 1 0
3 2 0
2 3 0
4 4 2
5 5 2

Answer 1

There are a couple of non-trivial things in this request. First is to order the resulting rows by the document position, which is not visible when you use OPENJSON … WITH to project the columns. And the second one is that you need a hierarchical query (assuming there could be multiple levels).
Anyway, something like this:
declare #doc nvarchar(max) = N'[{"id":1},{"id":3},{"id":2,"children":[{"id":4},{"id":5}]}]';
with q as
(
select [key] nodePath,
cast(json_value(d.[value],'$.id') as int) Id,
cast(null as int) ParentId,
cast(json_query(d.[value],'$.children') as nvarchar(max)) children
from openjson(#doc) d
union all
select q.nodePath + '.' + d.[key] nodePath,
cast(json_value(d.[value],'$.id') as int) Id,
q.id ParentId,
cast(json_query(d.[value],'$.children') as nvarchar(max)) children
from q
outer apply openjson(q.children) d
where q.children is not null
)
select Id, row_number() over (order by nodePath) [Order/Index], ParentId
from q
order by [Order/Index]
outputs
Id Order/Index ParentId
----------- -------------------- -----------
1 1 NULL
3 2 NULL
2 3 NULL
4 4 2
5 5 2
(5 rows affected)