您如何使用T-SQL獲得滿足條件的最大/最大數量的順序/連續記錄

Question

簡而言之，我希望創建一個查詢，以幫助我找到音樂會類型場地的最佳可用座位，就像Ticketmaster.com的“查找最佳可用座位”一樣，其中要求是找到最靠近舞台的所需座位數並且座位必須按順序排列。

給定此示例表：

DECLARE @Seats TABLE
(
    SectionId   INT         NOT NULL,
    RowId       VARCHAR(2)  NOT NULL,
    SeatId      INT         NOT NULL,
    Priority    INT         NOT NULL, /* Used to determine closeness to the stage and/or order to search in */
    StatusCd    CHAR(1)     NOT NULL, /* A for Available, H for Held, P for Purchased, etc. */
    Cost        MONEY       NOT NULL
)

並給出以下腳本來填充表：

DECLARE @SectionCounter INT
DECLARE @RowCounter INT
DECLARE @SeatCounter INT

SET     @SectionCounter = 1
SET     @RowCounter = 1

WHILE   @SectionCounter <= 10
BEGIN

    WHILE   @RowCounter <= 26
    BEGIN

        SET @SeatCounter = 1

        WHILE @SeatCounter <= 26
        BEGIN       

            INSERT INTO @Seats
            ( SectionId ,
              RowId ,
              SeatId ,
              Priority ,
              StatusCd ,
              Cost
            )
            VALUES 
            ( @SectionCounter ,
              CHAR(64 + @RowCounter) ,
              @SeatCounter ,
              1 ,
              (
                /* Randomly setting certain seats as purchased */
                SELECT  CASE
                        WHEN @SeatCounter IN 
                        (
                            1,2,9,10,
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0)),
                            (ROUND(((26 - 1 -1) * RAND() + 1), 0))
                        )
                        THEN 'P' ELSE 'A' END) ,
              (
                SELECT  CASE
                        WHEN @SectionCounter IN (1,2)
                        THEN 75.00 ELSE 25.00 END
              )
            )

            SET @SeatCounter = @SeatCounter + 1

        END

        SET @RowCounter = @RowCounter + 1

    END

    SET     @RowCounter = 1
    SET @SectionCounter = @SectionCounter + 1

END

查找x個連續/連續座位的最佳查詢是什么？

以下是我當前的解決方案，該應用程序至少需要3個查詢。

例如，如果客戶請求了下一個最佳可用座位中的8個，我將運行以下查詢：

/* Get each sections available seat count */
SELECT  SectionId,
        Priority,
        COUNT(SeatId) AS 'Seat Count'
FROM    @Seats
WHERE   StatusCd = 'A' /* A = Available. */
GROUP BY SectionId, Priority
ORDER BY Priority

這將產生如下結果集：

| SectionId | Priority | SeatCount |
|-----------|----------|-----------|
| 1         | 1        | 544       |
| 2         | 2        | 554       |
| 3         | 3        | 552       |

應用程序將顯示“是否有8個席位，優先級為1？” 並使用上面的結果集，答案是肯定的，因此讓我們獲取相應部分（即第1部分）的可用行數。這是該部分的查詢：

SELECT  RowId,
        COUNT(SeatId) AS 'Seat Count'
FROM    @Seats
WHERE   SectionId = 1
        AND StatusCd = 'A'
GROUP BY RowId

這將產生如下結果集：

| RowId | SeatCount |
|-------|-----------|
| A     | 21        |
| B     | 18        |
| C     | 22        |

應用程序將查看這些結果，並從第一行開始詢問相同的問題：“ A行中有8個席位嗎？” 根據以上結果，答案是肯定的，因此當時應用程序將使用此查詢來查詢A行中的所有席位：

SELECT  *
FROM    @Seats
WHERE   SectionId = 1
AND     RowId = 'A'

這將產生如下結果集：

| SectionId | RowId | SeatId | Priority | StatusCd | Cost  |
|-----------|-------|--------|----------|----------|-------|
| 1         | A     | 1      | 1        | P        | 75.00 |
| 1         | A     | 2      | 1        | P        | 75.00 |
| 1         | A     | 3      | 1        | A        | 75.00 |
| 1         | A     | 4      | 1        | A        | 75.00 |
| 1         | A     | 5      | 1        | A        | 75.00 |

那時，應用程序將遍歷結果，嘗試連續查找8個席位，且StatusCd為“ A”。

我敢肯定，有一種查詢數據庫中順序記錄的更有效的方法，而不必加載整個行並在代碼中完成。

我對最佳解決方案的最佳猜測是在桌子上進行自我連接，並對SeatId進行某種形式的增量或沿這些直線進行某種方式。

任何幫助或建議，我們將不勝感激。

Answer 1

這應該使您入門。 就自我加入而言，您處在正確的軌道上，這是另一種方式。

這將為您提供具有相同優先級，部分，行的前8個座位，狀態按優先級，部分，行的先后順序顯示為“ A”。 如果我誤會了什么，請糾正我。

DECLARE @number_seats AS INTEGER = 8;

WITH T1 AS (
    SELECT S.*,
           SeatId - ROW_NUMBER() OVER(PARTITION BY Priority, SectionId, RowId, StatusCd ORDER BY SeatId) AS grp
    FROM #seats AS S
),

T2 AS (
SELECT Priority    AS Priority,
       SectionId   AS Section,
       RowId       AS RowId,
       StatusCd    AS StatusCd, 
       MIN(SeatId) AS StartingSeat,
       MAX(SeatId) AS EndingSeat,
       COUNT(*)    AS Seats       
FROM T1
GROUP BY Priority, SectionId, RowId, StatusCd, grp
),

T3 AS (
    SELECT TOP 1 *
    FROM T2
    WHERE T2.Seats >= @number_seats and StatusCd = 'A'
    ORDER BY Priority, Section, RowId, StartingSeat
)
SELECT S.*
FROM T3 JOIN #seats AS S ON 
(
    T3.Priority = S.Priority AND
    T3.Section  = S.SectionId AND
    T3.RowId    = S.RowId AND
    S.SeatId BETWEEN T3.StartingSeat AND T3.StartingSeat + @number_seats - 1
)
ORDER BY Priority, Section, RowId, StartingSeat

結果：

SectionId   RowId SeatId      Priority    StatusCd Cost
----------- ----- ----------- ----------- -------- ---------------------
1           A     11          1           A        75.00
1           A     12          1           A        75.00
1           A     13          1           A        75.00
1           A     14          1           A        75.00
1           A     15          1           A        75.00
1           A     16          1           A        75.00
1           A     17          1           A        75.00
1           A     18          1           A        75.00