从SQL Server中选择记录，例如下面的数据

Question

I have record like below in SQL Server.

 Id    RefId    FromRefId 
  1     RH01    RH00 
  2     RH02    RH01 
  3     RH03    RH01 
  4     RH04    RH03
  5     RH05    RH02 
  6     RH06    RH03 
  7     RH07    RH04 
  8     RH08    RH02 
  9     RH09    RH05

And I want get result like below using Id in where condition

Where Id=1
RH02
RH03
RH04
RH05
RH06
RH07
RH08
RH09

Where Id=2
RH05
RH08
RH09

Where Id=3
RH04
RH06
RH07

Where Id=4
RH07

Where Id=5
RH09

Thanks, please guide me how can I achieve this?

Answer 1

Since you want to obtain all the references following the chain of FromRefId you need to use a recursive query, which can be achieved in SQL Server using a recursive common table expression :

with Recursive_IDs (Id, RefId, FromRefId) as (
  -- anchor query
  select Id, RefId, FromRefId
  from IDs

  union all

  -- recursive query
  select IDs.Id, IDs.RefID, Recursive_IDs.FromRefId
  from IDs
  inner join Recursive_IDs on Recursive_IDs.RefId=IDs.FromRefId
)
select Recursive_IDs.RefId
from Recursive_IDs
join IDs on Recursive_IDs.FromRefID=IDs.RefID
where IDs.id = [the id you want]

SQL fiddle

Note that if instead of searching by Id you search by RefId you can simplify the query a bit:

with Recursive_IDs (Id, RefId, FromRefId) as (
  -- anchor query
  select Id, RefId, FromRefId
  from IDs

  union all

  -- recursive query
  select IDs.Id, IDs.RefID, Recursive_IDs.FromRefId
  from IDs
  inner join Recursive_IDs on Recursive_IDs.RefId=IDs.FromRefId
)
select Recursive_IDs.RefId
from Recursive_IDs
where FromRefId = [the RefId you want]

Answer 2

You can use the below approach. I have written a Table-valued function, "GetChild". It iterates through the records recursively to get all dependencies, and finally get the RefId for all those dependencies.

Create table hierarchy (Id int, RefId varchar(10), FromRefId varchar(10))
GO
insert into hierarchy
select   1,'RH01','RH00'  union all
select  2,'RH02','RH01'  union all
select  3,'RH03','RH01'  union all 
select  4,'RH04','RH03'  union all
select  5,'RH05','RH02'  union all 
select  6,'RH06','RH03'  union all 
select  7,'RH07','RH04'  union all 
select  8,'RH08','RH02'  union all 
select  9,'RH09','RH05'

GO
-- Table valued Function
GO
create function GetChild (@Id INT)
RETURNS @temp TABLE (RefId varchar(10))
AS
BEGIN

    declare @tempDependencies table (Id int)
    insert into @tempDependencies SELECT @Id

    WHILE ((Select COUNT(Id) from hierarchy where FromRefId in (select RefId from hierarchy where id in (select Id from @tempDependencies) ) and id not in (select Id from @tempDependencies)) > 0)
      BEGIN
      insert into @tempDependencies 
      Select Id from hierarchy where FromRefId in (select RefId from hierarchy where id in (select Id from @tempDependencies) ) and id not in (select Id from @tempDependencies)
      END

    insert into @temp 
    Select RefId from hierarchy where FromRefId in (select RefId from hierarchy where id in (SELECT Id from @tempDependencies))


    return 
END
GO


-- You may call the functions like this:

select * from GetChild(1)
select * from GetChild(2)
select * from GetChild(3)

SQL Fiddle Code

Answer 3

Should be a simple query

SELECT * FROM your_table_name WHERE Id = your_desired_id

Why the downgrade? Isn't that what you were looking for? I don't think your question is clear. Which Id is being referred here?!