Question

In my table each record has a pointer to his direct parent and I need to know how to query for all the descendants, direct or not (the son of a son), of a given record.

Facts:

• I don’t know how deep the tree is and i need all the leafs
• Some records might not have a child record
• I’m running under SqlServer 2012

Can anyone tell me how to write such a query?

Answer 1

Building on the query from Josh Wallace, to get descendents.

declare @people table
(
    Id int,
    Name nvarchar(50),
    ParentId int
)

insert into @people values (1, 'Frank', null)
insert into @people values (2, 'Shane', null)
insert into @people values (3, 'George', 1)
insert into @people values (5, 'Hank', 1)
insert into @people values (7, 'Abigail', 3)
insert into @people values (8, 'Ben', 3)
insert into @people values (9, 'Charlie', 5)
insert into @people values (10, 'Dave', 5)
insert into @people values (11, 'Homer', 5)
insert into @people values (12, 'Junebug', 7)
insert into @people values (13, 'Bart', 11)
insert into @people values (14, 'Lisa', 11)


;with descendents AS (
    -- Anchor member definition
    select p.Id, p.Name, p.ParentId, Level = 0 
    from @people p 
    where p.Id = 1 -- person to search for descendents 

    union all

    -- Recursive member definition
    select p.Id, p.Name, p.ParentId, Level + 1
    from @people p 
    inner join descendents a on p.ParentId = a.Id
)


select 
    a.Level, ParentID = p.Id, Parent = p.Name, a.Id, Child = a.Name
from descendents a 
    left join @people p on p.Id = a.ParentId
order by a.Level