Recursive select in SQL

问题

I have an issue I just can't get my head around. I know what I want, just simply can't get it out on the screen. What I have is a table looking like this:

Id, PK UniqueIdentifier, NotNull
Name, nvarchar(255), NotNull
ParentId, UniqueIdentifier, Null

ParentId have a FK to Id.

What I want to accomplish is to get a flat list of all the id's below the Id I pass in.

example:

1   TestName1    NULL
2   TestName2    1
3   TestName3    2
4   TestName4    NULL
5   TestName5    1

The tree would look like this:

-1
  -> -2
       -> -3
  -> -5
-4

If I now ask for 4, I would only get 4 back, but if I ask for 1 I would get 1, 2, 3 and 5. If I ask for 2, I would get 2 and 3 and so on.

Is there anyone who can point me in the right direction. My brain is fried so I appreciate all help I can get.

回答1:

declare @T table(
  Id int primary key,
  Name nvarchar(255) not null,
  ParentId int)

insert into @T values
(1,   'TestName1',    NULL),
(2,   'TestName2',    1),
(3,   'TestName3',    2),
(4,   'TestName4',    NULL),
(5,   'TestName5',    1)

declare @Id int = 1

;with cte as
(  
  select T.*
  from @T as T
  where T.Id = @Id
  union all
  select T.*
  from @T as T
    inner join cte as C
      on T.ParentId = C.Id
)
select *
from cte

Result

Id          Name                 ParentId
----------- -------------------- -----------
1           TestName1            NULL
2           TestName2            1
5           TestName5            1
3           TestName3            2

回答2:

Here's a working example:

declare @t table (id int, name nvarchar(255), ParentID int)

insert @t values
(1,   'TestName1',    NULL),
(2,   'TestName2',    1   ),
(3,   'TestName3',    2   ),
(4,   'TestName4',    NULL),
(5,   'TestName5',    1   );

; with rec as
        (
        select  t.name
        ,       t.id as baseid
        ,       t.id
        ,       t.parentid
        from    @t t
        union all
        select  t.name
        ,       r.baseid
        ,       t.id
        ,       t.parentid
        from    rec r
        join    @t t
        on      t.ParentID = r.id
        )
select  *
from    rec
where   baseid = 1

You can filter on baseid, which contains the start of the tree you're querying for.

回答3:

Try this:

WITH RecQry AS
(
    SELECT *
      FROM MyTable
    UNION ALL
    SELECT a.*
      FROM MyTable a INNER JOIN RecQry b
        ON a.ParentID = b.Id
)
SELECT *
  FROM RecQry

回答4:

Here is a good article about Hierarchy ID models. It goes right from the start of the data right through to the query designs.

Also, you could use a Recursive Query using a Common Table Expression.

回答5:

I'm guessing that the easiest way to accomplish what you're looking for would be to write a recursive query using a Common Table Expression:

MSDN - Recursive Queries Using Common Table Expressions

来源：https://stackoverflow.com/questions/5649446/recursive-select-in-sql

标签

sql

sql-server-2008

recursive-query