130.最短乘车路线查询-案例

CREATE TABLE T_Line(
ID      nvarchar(10),  --公交线路号
Station nvarchar(10),  --站点名称
Orders  int)           --行车方向(通过它反应每个站的上一个、下一个站)
INSERT T_Line 
SELECT N'8路'  ,N'站A',1 UNION ALL
SELECT N'8路'  ,N'站B',2 UNION ALL
SELECT N'8路'  ,N'站C',3 UNION ALL
SELECT N'8路'  ,N'站D',4 UNION ALL
SELECT N'8路'  ,N'站J',5 UNION ALL
SELECT N'8路'  ,N'站L',6 UNION ALL
SELECT N'8路'  ,N'站M',7 UNION ALL
SELECT N'20路' ,N'站G',1 UNION ALL
SELECT N'20路' ,N'站H',2 UNION ALL
SELECT N'20路' ,N'站I',3 UNION ALL
SELECT N'20路' ,N'站J',4 UNION ALL
SELECT N'20路' ,N'站L',5 UNION ALL
SELECT N'20路' ,N'站M',6 UNION ALL
SELECT N'255路',N'站N',1 UNION ALL
SELECT N'255路',N'站O',2 UNION ALL
SELECT N'255路',N'站P',3 UNION ALL
SELECT N'255路',N'站Q',4 UNION ALL
SELECT N'255路',N'站J',5 UNION ALL
SELECT N'255路',N'站D',6 UNION ALL
SELECT N'255路',N'站E',7 UNION ALL
SELECT N'255路',N'站F',8
GO

--乘车线路查询存储过程
CREATE PROC p_qry
@Station_Start nvarchar(10),
@Station_Stop  nvarchar(10)
AS
SET NOCOUNT ON
DECLARE @l int
SET @l=0
SELECT ID,Station,
	Line=CAST('('+RTRIM(ID)+': '+RTRIM(Station) as nvarchar(4000)),
	Orders=Orders,
	[Level]=@l
INTO # FROM T_Line
WHERE Station=@Station_Start
WHILE @@ROWCOUNT>0 
	AND NOT EXISTS(SELECT * FROM # WHERE Station=@Station_Stop)
BEGIN
	SET @l=@l+1
	INSERT #(Line,ID,Station,Orders,[Level])
	SELECT 
		Line=a.Line+CASE
			WHEN a.ID=b.ID THEN N'->'+RTRIM(b.Station)
			ELSE N') ∝ ('+RTRIM(b.ID)
				+N': '+RTRIM(b.Station) END,
		b.ID,b.Station,b.Orders,@l
	FROM # a,T_Line b
	WHERE a.[Level]=@l-1
		AND(a.Station=b.Station AND a.ID<>b.ID
			OR a.ID=b.ID AND(
				a.Orders=b.Orders+1
				OR
				a.Orders=b.Orders-1))
		AND LEN(a.Line)<4000
		AND PATINDEX('%[ >]'+b.Station+'[-)]%',a.Line)=0
END
SELECT N'起点站'=@Station_Start
	,N'终点站'=@Station_Stop
	,N'乘车线路'=Line+N')' 
FROM # 
WHERE [Level]=@l 
	AND Station=@Station_Stop
IF @@ROWCOUNT =0 --如果未有可以到达的线路,则显示处理结果表备查
	SELECT * FROM #
GO

--调用
EXEC p_qry N'站A',N'站L'
/*--结果
起点站  终点站  乘车线路
---------- ------------ -----------------------------------------------------------
站A    站L    (8路: 站A->站B->站C->站D->站J->站L)
--*/