遞歸查詢對(duì)于同一個(gè)表父子關(guān)系的計(jì)算提供了很大的方便，這個(gè)示例使用了SQL server 2005中的遞歸查詢,使用的表是CarParts，這個(gè)表存儲(chǔ)了一輛汽車的所有零件以及結(jié)構(gòu)，part為零件單位，subpart為子零件，Qty為數(shù)量。

具體示例如下：

*/

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

/*

一輛汽車需要各個(gè)零件的數(shù)目

1個(gè)Body 需要4個(gè)Door

1個(gè)Door 需要1個(gè)Mirror

那么

1個(gè)body需要4個(gè)Mirror

結(jié)構(gòu)很簡單吧

*/

WITH CarPartsCTE(SubPart, Qty)

AS

(

-- 固定成員 (AM):

-- SELECT查詢無需參考CarPartsCTE

-- 遞歸從此處開始

SELECT SubPart, Qty

FROM CarParts

WHERE Part = 'Body'

UNION ALL

-- 遞歸成員 (RM):

-- SELECT查詢參考CarPartsCTE

-- 使用現(xiàn)有數(shù)據(jù)往下一層展開

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

/*

注意看最下層的small_Mirror 位于 表最后的位置，

由此可以看出改遞歸不是開始就進(jìn)行遞歸查詢而是在1層完全展開后在根據(jù)該層展開下一層不是深度優(yōu)先的遞歸

*/

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：

以下示例顯示經(jīng)理以及向經(jīng)理報(bào)告的雇員的層次列表。

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