SQL Server 2005数据库中表的递归查询
递归查询对于同一个表父子关系的计算提供了很大的方便，这个示例使用了SQL server 2005中的递归查询,使用的表是CarParts，这个表存储了一辆汽车的所有零件以及结构，part为零件单位，subpart为子零件，Qty为数量。
具体示例如下：
*/
CREATE TABLE CarParts
(
CarID INT NOT NULL,
Part VARCHAR(15),
SubPart VARCHAR(15),
Qty INT
)
GO
INSERT CarParts VALUES (1, ''Body'', ''Door'', 4)
INSERT CarParts VALUES (1, ''Body'', ''Trunk Lid'', 1)
INSERT CarParts VALUES (1, ''Body'', ''Car Hood'', 1)
INSERT CarParts VALUES (1, ''Door'', ''Handle'', 1)
INSERT CarParts VALUES (1, ''Door'', ''Lock'', 1)
INSERT CarParts VALUES (1, ''Door'', ''Window'', 1)
INSERT CarParts VALUES (1, ''Body'', ''Rivets'', 1000)
INSERT CarParts VALUES (1, ''Door'', ''Rivets'', 100)
INSERT CarParts VALUES (1, ''Door'', ''Mirror'', 1)
INSERT CarParts VALUES (1, ''Mirror'', ''small_Mirror'', 4)
GO
SELECT * FROM CarParts
GO
/*
一辆汽车需要各个零件的数目
1个Body 需要4个Door
1个Door 需要1个Mirror
那么
1个body需要4个Mirror
结构很简单吧
*/
WITH CarPartsCTE(SubPart, Qty)
AS
(
-- 固定成员 (AM):
-- SELECT查询无需参考CarPartsCTE
-- 递归从此处开始
SELECT SubPart, Qty
FROM CarParts
WHERE Part = ''Body''
UNION ALL
-- 递归成员 (RM):
-- SELECT查询参考CarPartsCTE
-- 使用现有数据往下一层展开
SELECT CarParts.SubPart, CarPartsCTE.Qty * CarParts.Qty
FROM CarPartsCTE
INNER JOIN CarParts ON CarPartsCTE.SubPart = CarParts.Part
WHERE CarParts.CarID = 1
)
SELECT SubPart,Qty AS TotalNUM
FROM CarPartsCTE
/*
注意看最下层的small_Mirror 位于 表最后的位置，
由此可以看出改递归不是开始就进行递归查询而是在1层完全展开后在根据该层展开下一层不是深度优先的递归
*/
drop table CarParts
--------------------------------result---------------------------------------
CarID Part SubPart Qty
----------- --------------- --------------- -----------
1 Body Door 4
1 Body Trunk Lid 1
1 Body Car Hood 1
1 Door Handle 1
1 Door Lock 1
1 Door Window 1
1 Body Rivets 1000
1 Door Rivets 100
1 Door Mirror 1
1 Mirror small_Mirror 4
(10 row(s) affected)
SubPart TotalNUM
--------------- -----------
Door 4
Trunk Lid 1
Car Hood 1
Rivets 1000
Handle 4
Lock 4
Window 4
Rivets 400
Mirror 4
small_Mirror 16
(10 row(s) affected)
示例：
以下示例显示经理以及向经理报告的雇员的层次列表。
WITH DirectReports(groupid, member, EmployeeLevel,type) AS
(
SELECT groupid, member, 0,type AS EmployeeLevel
FROM groupinfo
WHERE groupid = ''finance_company''
UNION ALL
SELECT e.groupid, e.member, EmployeeLevel + 1,e.type
FROM groupinfo e
INNER JOIN DirectReports d
ON e.groupid = d.member
)
SELECT b.nickname,groupid, member, EmployeeLevel,type
FROM DirectReports,userbasicinfo b
where DirectReports.member=b.id
and type = 1