How to generate hierarchical JSON data with Microsoft SQL Server 2016?

Question

I\'m using Microsoft SQL Server 2016. This version supports JSON.

I have a Person table with the following data:

Pe         


        

Answer 1

Unfortunately, recursive CTe cannot be used to generate hierarchical json . Output of recursive CTE is still flat result.

The only way to create hierarchical output is to create separate CTE for each level and then join the using FOR JSON AUTO

Prepare table:

declare @t table (PersonId int, FatherId int, Name nvarchar(20));

insert into @t(PersonId, FatherId, Name)
values
(1, NULL, '4th Grand Father'),
(2, 1, '3rd Grand Father'),
(3, 2, '2nd Grand Father'),
(4, 3, 'Grand Father'),
(5, 4, 'Father'),
(6, 4, 'Uncle'),
(7, 6, 'Cousin'),
(8, 5, 'Brother'),
(9, 5, 'Me');

-- Hierarchical query:

WITH
Persons_CTE1 AS(
    SELECT PersonId, FatherId, Name FROM @t WHERE FatherId IS NULL
),
Persons_CTE2 AS(
    SELECT P.PersonId, P.FatherId, P.Name
    from @t P
    WHERE P.FatherId IN (SELECT PersonId FROM Persons_CTE1)
),
Persons_CTE3 AS(
    SELECT P.PersonId, P.FatherId, P.Name
    from @t P
    WHERE P.FatherId IN (SELECT PersonId FROM Persons_CTE2)
),
Persons_CTE4 AS(
    SELECT P.PersonId, P.FatherId, P.Name
    from @t P
    WHERE P.FatherId IN (SELECT PersonId FROM Persons_CTE3)
),
Persons_CTE5 AS(
    SELECT P.PersonId, P.FatherId, P.Name
    from @t P
    WHERE P.FatherId IN (SELECT PersonId FROM Persons_CTE4)
),
Persons_CTE6 AS(
    SELECT P.PersonId, P.FatherId, P.Name
    from @t P
    WHERE P.FatherId IN (SELECT PersonId FROM Persons_CTE5)
)
select Persons_CTE1.Name, Persons_CTE2.Name, Persons_CTE3.Name,
       Persons_CTE4.Name, Persons_CTE5.Name, Persons_CTE6.Name
from Persons_CTE1
    LEFT JOIN Persons_CTE2
        ON Persons_CTE2.FatherId = Persons_CTE1.PersonId
    LEFT JOIN Persons_CTE3
        ON Persons_CTE3.FatherId = Persons_CTE2.PersonId
    LEFT JOIN Persons_CTE4
        ON Persons_CTE4.FatherId = Persons_CTE3.PersonId
    LEFT JOIN Persons_CTE5
        ON Persons_CTE5.FatherId = Persons_CTE4.PersonId
    LEFT JOIN Persons_CTE6
        ON Persons_CTE6.FatherId = Persons_CTE5.PersonId
FOR JSON AUTO