数据层次结构建模之一

1,在现实世界中，有很多现象存在层次结构，公司的人事职称是典型的层次结果，如下图

Sql Server是关系型DB，适合存储二维关系的数据，如何存储具有层次结构的数据了？需要使用一个字段ParentID表示上级ID，示例表结构如下

create table dbo.emph

(

ID int not null primary key,

ParentID int foreign key references dbo.emph(id),

Descr varchar(100) not null

)

2,插入示例数据

insert into dbo.emph(id,ParentID,Descr)

values(1,null,'boss'),

(2,1,'M1'),(3,1,'M2'),(4,1,'M3'),(5,1,'M4'),

(6,2,'L11'),(20,2,'L12'),(7,2,'L13'),(8,2,'L14'),(9,2,'L15'),

(10,3,'L21'),(11,3,'L22'),(12,3,'L23'),(14,3,'L24'),

(15,6,'E111'),(16,6,'E112'),(17,6,'E113'),(18,6,'E114'),

(19,20,'E121'),(21,20,'E122'),(22,20,'E123')

3,使用CTE递归查询M1手下的所有员工，包括Leader和Employee

;with cte(id,parentid,descr) as

(

select id,parentid,descr

from dbo.emph 

where id=2

union all

select e.ID,e.ParentID,e.Descr

from dbo.emph e

inner join cte c on e.ParentID=c.id

)

select *

from cte

order by parentid

4,查看查询嵌套的Level，示例代码如下

;with cte(id,parentid,descr,Level) as

(

select id,parentid,descr,0 as Level

from dbo.emph 

where id=2

union all

select e.ID,e.ParentID,e.Descr,Level+1 as Level

from dbo.emph e

inner join cte c on e.ParentID=c.id

)

select *

from cte

order by parentid

5,查看每一行数据的Path，便于查看归属关系，path是使用ID来界定的

;with cte(path,id,parentid,descr,Level) as

(

select cast('\'+cast(id as varchar) as varchar(100)) as path, 

　　id,parentid,descr,0 as Level

from dbo.emph 

where id=2

union all

select cast(c.path+'\'+ cast(e.ID as varchar) as varchar(100)) as path, 

    e.ID,e.ParentID,e.Descr,Level+1 as Level

from dbo.emph e

inner join cte c on e.ParentID=c.id

)

select *

from cte

order by parentid

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