SQL实现最优坐地铁方案

网络整理 - 07-27

坐地铁有时候不一定要坐最少站的，有时是希望能坐换乘次数最少的，应该怎么改造才能把所有的方案都取出来，然后按换乘次数、经过站点数依次排序?

　　lineID state orderid

　　1 广州东 1

　　1 体育中心2

　　1 体育西 3

　　1 烈士陵园4

　　1 公园前 6

　　1 西门口 7

　　2 火车站 1

　　2 纪念堂 2

　　2 公园前 3

　　2 中大 4

　　2 客村 5

　　2 琶洲 6

　　2 万胜围 7

　　3 广州东 1

　　3 体育西 2

　　3 珠江新城3

　　3 客村 4

　　3 市桥 5

　　4 万胜围 1

　　4 金洲 2

　　如上面数据，想查询“广州东”至“中大”，大家通过程序计算列出全部的方案。

　Peak Wong：

　　SQL code　　

DECLARE @tb TABLE(
lineID int, state nvarchar(10), orderid int)
INSERT @tb
SELECT 1, N'广州东', 1 UNION ALL
SELECT 1, N'体育中心', 2 UNION ALL
SELECT 1, N'体育西', 3 UNION ALL
SELECT 1, N'烈士陵园', 4 UNION ALL
SELECT 1, N'公园前', 6 UNION ALL
SELECT 1, N'西门口', 7 UNION ALL
SELECT 2, N'火车站', 1 UNION ALL
SELECT 2, N'纪念堂', 2 UNION ALL
SELECT 2, N'公园前', 3 UNION ALL
SELECT 2, N'中大', 4 UNION ALL
SELECT 2, N'客村', 5 UNION ALL
SELECT 2, N'琶洲', 6 UNION ALL
SELECT 2, N'万胜围', 7 UNION ALL
SELECT 3, N'广州东', 1 UNION ALL
SELECT 3, N'体育西', 2 UNION ALL
SELECT 3, N'珠江新城', 3 UNION ALL
SELECT 3, N'客村', 4 UNION ALL
SELECT 3, N'市桥', 5 UNION ALL
SELECT 4, N'万胜围', 1 UNION ALL
SELECT 4, N'金洲', 2

DECLARE
    @state_start nvarchar(10),
    @state_stop nvarchar(10)
SELECT
    @state_start = N'广州东',
    @state_stop = N'中大'

-- 查询
DECLARE @re TABLE(
    path nvarchar(max),
    state_count int,
    start_lineID int,
    start_state nvarchar(10),
    current_lineID int,
    current_state nvarchar(10),
    current_orderid int,
    flag int,
    lineIDs nvarchar(max),
    level int
)
DECLARE
    @level int,
    @rows int
SET
    @level = 0

-- 开始
INSERT @re
SELECT
    path = CONVERT(nvarchar(max),
            RTRIM(A.lineID) + N'{'
                + RTRIM(A.orderid) + N'.' + A.state
        ),
    state_count = 0,
    start_lineID = A.lineID,
    start_state = A.state,
    current_lineID = A.lineID,
    current_state = A.state,
    current_orderid = A.orderid,
    flag = CASE
            WHEN A.state = @state_stop THEN 0
            ELSE NULL END,
    lineIDs = ',' + RTRIM(A.lineID) + ',',
    level = -(@level + 1)
FROM @tb A
WHERE state = @state_start
SET @rows = @@ROWCOUNT
WHILE @rows > 0
BEGIN
    SELECT
        @level = @level + 1
    INSERT @re
    -- 同一 LineID
    SELECT
        path = CONVERT(nvarchar(max),
                A.path
                    + N'->'
                    + RTRIM(B.orderid) + N'.' + B.state
             ),
        state_count = A.state_count + 1,
        A.start_lineID, A.start_state,
        current_lineID = B.lineID,
        current_state = B.state,
        current_orderid = B.orderid,
        flag = CASE
                WHEN B.state = @state_stop THEN 0
                ELSE A.flag END,
        A.lineIDs,
        level = @level
    FROM @re A, @tb B
    WHERE A.flag <> 0
        AND A.level = @level - 1
        AND A.current_lineID = B.lineID
        AND A.current_orderid + A.flag = B.orderid

    UNION ALL
    -- 不同 LineID
    SELECT
        path = CONVERT(nvarchar(max),
                A.path + N')->'
                    + RTRIM(B.lineID) + N'{'
                    + RTRIM(B.orderid) + N'.' + B.state
             ),
        state_count = A.state_count + 1,
        A.start_lineID, A.start_state,
        current_lineID = B.lineID,
        current_state = B.state,
        current_orderid = B.orderid,
        flag = CASE
                WHEN B.state = @state_stop THEN 0
                ELSE NULL END,
        A.lineIDs + RTRIM(B.lineID) + ',',
        level = - @level
    FROM @re A, @tb B
    WHERE A.flag <> 0
        AND state_count = @level - 1
        AND A.current_lineID <> B.lineID
        AND A.current_state = B.state
        AND NOT EXISTS(
                SELECT * FROM @re
                WHERE CHARINDEX(',' + RTRIM(B.lineID) + ',', A.lineIDs) > 0)
    SET @rows = @@ROWCOUNT

    INSERT @re
    -- 不同 LineID 的第1站正向
    SELECT
        path = CONVERT(nvarchar(max),
                A.path
                    + N'->'
                    + RTRIM(B.orderid) + N'.' + B.state
            ),
        state_count = A.state_count + 1,
        A.start_lineID, A.start_state,
        current_lineID = B.lineID,
        current_state = B.state,
        current_orderid = B.orderid,
        flag = CASE
                WHEN B.state = @state_stop THEN 0
                ELSE 1 END,
        A.lineIDs,
        level = @level
    FROM @re A, @tb B
    WHERE A.flag IS NULL
        AND A.level = - @level
        AND A.current_lineID = B.lineID
        AND A.current_orderid + 1 = B.orderid
    UNION ALL
    -- 不同 LineID 的第1站反向
    SELECT
        path = CONVERT(nvarchar(max),
                A.path
                    + N'->'
                    + RTRIM(B.orderid) + N'.' + B.state
            ),
        state_count = A.state_count + 1,
        A.start_lineID, A.start_state,
        current_lineID = B.lineID,
        current_state = B.state,
        current_orderid = B.orderid,
        flag = CASE
                WHEN B.state = @state_stop THEN 0
                ELSE - 1 END,
        A.lineIDs,
        level = @level
    FROM @re A, @tb B
    WHERE A.flag IS NULL
        AND A.level = - @level
        AND A.current_lineID = B.lineID
        AND A.current_orderid - 1 = B.orderid

SET @rows = @rows + @@ROWCOUNT
END

SELECT
--    *,
    path = path + N'}',
    state_count
FROM @re
WHERE flag = 0

　　结果(数字5,7是要经过多少站:

　　3{1.广州东-> 2.体育西-> 3.珠江新城-> 4.客村)-> 2{5.客村-> 4.中大} 5

　　1{1.广州东-> 2.体育中心-> 3.体育西)-> 3{2.体育西-> 3.珠江新城-> 4.客村)-> 2{5.客村-> 4.中大} 7