运行总计，直到特定条件为真

Question

我有一个 table 代表发牌人的牌及其等级。我现在正在尝试（尽可能快地）查询以设置游戏状态。

(As said before, only the dealer cards is shown)
W = Win
S = Stand
L = Loss
B = Blackjack (in two cards)

关于规则：庄家在 21 点赢，如果有两张牌就是 21 点。如果排名在 17 到 20 之间，则 S = stand。超过21岁就输了。

排名：

1 (ACE) - 1 or 11 rank. Counted as 11.

2-10 - 2-10 rank

11-13 (knight - king) - 10 rank

╔════╦══════╦════════╗
║ Id ║ Rank ║ Status ║
╠════╬══════╬════════╣
║  1 ║    1 ║        ║
║  2 ║    5 ║        ║
║  3 ║    8 ║ L      ║  //24 = Loss
║  4 ║    3 ║        ║
║  5 ║    1 ║        ║
║  6 ║    7 ║ W      ║  //21 = Win
║  7 ║   10 ║        ║
║  8 ║    1 ║ B      ║  //21 = Blackjack
║  9 ║   10 ║        ║
╚════╩══════╩════════╝

我尝试使用计数器来检查它是否是 21 点，然后我使用“RunningPoint”来检查牌的总和。

我现在有一个不好的解决方案，它在大量数据时显示出非常糟糕的性能。你会怎么做，我能做些什么来优化我的查询？当使用更多数据时，我还需要使用选项 (maxrecursion 0)

（当有 100 万行时，甚至不可能运行这个...）

我的例子：http://sqlfiddle.com/#!6/3855e/1

Answer 1

此解决方案基于古怪更新。更多信息 here.

LiveDemo

数据和结构：

CREATE TABLE #BlackJack
(
   id INT 
  ,Rank INT
  ,running_total INT
  ,result NVARCHAR(100)
);

CREATE CLUSTERED INDEX IX_ROW_NUM ON #BlackJack(id);

insert into #BlackJack (Id, Rank)
values (1, 1),(2, 5), (3, 8), (4, 3), (5, 1),
       (6, 7), (7, 10), (8, 1),(9, 10), (10, 10), (11,1);

主查询：

DECLARE @running_total       INT = 0
        ,@number_of_cards    INT = 0
        ,@prev_running_total INT = 0;

UPDATE #BlackJack
SET 
   @prev_running_total = @running_total
  ,@running_total = running_total = IIF(@running_total >= 20, 0, @running_total) 
                                    + CHOOSE(Rank,11,2,3,4,5,6,7,8,9,10,10,10,10)
  ,result        = CASE WHEN @running_total = 20 THEN 'S'
                        WHEN @running_total = 21 AND @number_of_cards = 2 THEN 'B'
                        WHEN @running_total = 21 THEN 'W'
                        WHEN @running_total > 21 THEN 'L'
                        ELSE NULL
                    END
  ,@number_of_cards  = IIF(@prev_running_total >= 20, 0, @number_of_cards) + 1
FROM #BlackJack WITH(INDEX(IX_ROW_NUM))
OPTION (MAXDOP 1);

SELECT *
FROM #BlackJack
ORDER BY id;

警告

如果您使用 SQL Server < 2012，则需要将 IIF 和 CHOOSE 替换为 CASE。我不检查所有二十一点规则，只检查提供的示例。如果出现问题，请随时更改 CASE 逻辑。

其次，我使用辅助列扩展基础 table BlackJack，但如果需要，您可以创建任何新的 table。

重点是按clustered key升序顺序读取数据，不允许并行执行。在生产中使用它之前，请检查它如何处理大型数据集。

Answer 2

没有使用普通 SQL 的有效解决方案（包括窗口化聚合函数），至少还没有人找到 :-)

你的递归查询执行不好，因为它太复杂了，这是一个简化版本：

编辑：修复了计算 (Fiddle)

WITH ctePoints AS
 (
   SELECT 1 AS id
        ,rank
        ,CASE 
           WHEN rank >= 10 THEN 10
           WHEN rank = 1 THEN 11
           ELSE rank
         END AS Point
        ,1 AS Counter
   FROM dbo.BlackJack
   WHERE Id = 1

   UNION ALL

   SELECT t2.Id
        ,t2.rank
        ,CASE WHEN t1.Point < 17 THEN t1.Point ELSE 0 END 
         + CASE 
             WHEN t2.rank >= 10 THEN 10
             WHEN t2.rank = 1 THEN 11
             ELSE t2.rank
           END AS Point
        ,CASE WHEN t1.Point < 17 THEN t1.Counter + 1 ELSE 1 END AS Counter
   FROM dbo.BlackJack AS t2
   INNER JOIN ctePoints AS t1 ON t2.Id = t1.Id + 1
 ) 
SELECT ctepoints.*
     ,CASE 
        WHEN Point < 17 THEN ''
        WHEN Point < 20 THEN 'S'
        WHEN Point > 21 THEN 'L'
        WHEN Point = 21 AND Counter = 2 THEN 'B'
        ELSE 'W' 
      END AS DealerStatus            
FROM ctePoints

它可能还是太慢了，因为它是逐行处理的。

我通常使用递归 SQL 来替换游标逻辑（因为在我的 DBMS 中它通常要快得多）但游标更新实际上可能更快 (Demo):

CREATE TABLE #BlackJack
(
   id INT PRIMARY KEY CLUSTERED
  ,Rank INT
  ,DealerStatus CHAR(1)
);

insert into #BlackJack (Id, Rank)
values 
(1, 1),(2, 5), (3, 8), (4, 3), (5, 1), (6, 7), (7, 10), (8, 1),(9, 10), (10, 10), (11,1);


DECLARE @Counter INT = 0
        ,@Point INT = 0
        ,@id int
        ,@Rank int
        ,@DealerStatus char(1)

DECLARE c CURSOR
FOR
SELECT id, Rank
FROM #BlackJack 
ORDER BY id FOR UPDATE OF DealerStatus

OPEN c

FETCH NEXT FROM c INTO @id, @Rank

WHILE @@FETCH_STATUS = 0
  BEGIN
    SET @counter = @counter + 1

    SET @Rank = CASE
                  WHEN @Rank >= 10 THEN 10
                  WHEN @Rank  = 1  THEN  11
                  ELSE @Rank
                END 

    SET @Point = @Point + @Rank

    SET @DealerStatus = CASE 
                          WHEN @Point < 17 THEN ''
                          WHEN @Point < 20 THEN 'S'
                          WHEN @Point > 21 THEN 'L'
                          WHEN @Point = 21 AND @Counter = 2 THEN 'B'
                          ELSE 'W' 
                        END 

    IF @Point >= 17 
    BEGIN
      UPDATE  #BlackJack 
      SET DealerStatus = @DealerStatus
      WHERE CURRENT OF c;

      SET @Point = 0

      SET @Counter = 0
    END

    FETCH NEXT FROM c INTO @id, @Rank
  END

CLOSE c
DEALLOCATE c

SELECT * FROM #BlackJack ORDER BY id

@lad2025 的 "quirky update" 仍然是获得预期结果的最快方法，但它使用了未记录的功能，如果 Service Pack 破坏了它，则没有办法抱怨它:-)

运行总计，直到特定条件为真

Running Total until specific condition is true

sql

tsql

sql-server

query-optimization

sql-server-2014

运行 总计，直到特定条件为真

Running Total until specific condition is true

sql

tsql

sql-server

query-optimization

sql-server-2014

运行总计，直到特定条件为真