SET ANSI_NULLS OFF
GO
SET QUOTED_IDENTIFIER OFF
GO

CREATE PROCEDURE [dbo].[UP_Department_GetAllChildDeptGUIDByLevels]
@DeptGUID uniqueidentifier,
@StartLevel int,
@EndLevel int
 AS
BEGIN
SET NOCOUNT ON

declare @str        varchar(8000)
Declare @sql        varchar(8000)
declare @str1       varchar(8000)
declare @str2       varchar(8000)
declare @CountBy    int
declare @i          int

set @i = 0
set @CountBy = dbo.DeptLevel_CountBy(@StartLevel,@EndLevel)
set @str1 = 'select guid from Department(nolock) where parentguid = '''+cast(@DeptGUID as varchar(50))+''''
set @str2 = 'select guid from Department(nolock) where parentguid in ('
set @str = @str1
set @sql = @str1

while @i < @CountBy
    begin
        set @str = @str2 + @str + ')'
        set @sql = @sql + ' union ' + @str
        set @i = @i + 1
    end
--print @sql
execute(@sql)

END

SET ANSI_NULLS OFF

CREATE FUNCTION [dbo].[DeptLevel_CountBy]
(
@StartLevel         int,
@EndLevel           int
)
RETURNS int
AS
BEGIN
DECLARE @CountBy int
 
    SELECT @CountBy=count(LevelCode)
    FROM DeptLevel
    WHERE LevelCode BETWEEN @StartLevel AND @EndLevel

RETURN @CountBy

END

其中LevelCode为部门的层级,此算法取得子部门ID后,怎么操作就看你了。
速度很快，适合大型企业。