Question

我正在使用 SQL Server 2016 并有一个包含以下数据的表：

<头>

PlaySeq	TransMaxValue
1	250
2	500
3	0
4	400
5	0
6	300
7	500
8	0
9	0

我正在尝试构建一个向该数据集添加列 TransMaxValueContd 的查询。
该 TransMaxValueContd 列应保留在列 TransMaxValue 中遇到的最后一个非零值。
订购由PlaySeq完成。

我预期的查询结果如下：

<头>

PlaySeq	TransMaxValue	TransMaxValueContd
1	250	250
2	500	500
3	0	500
4	400	400
5	0	400
6	300	300
7	500	500
8	0	500
9	0	500

我一直在使用像 LAST_VALUE() 和 LAG() 这样的窗口函数，但似乎无法得到正确的结果。
也许我把它复杂化了。
有人知道怎么做吗？

ps：我只是在寻找查询。无需修改源表。

编辑：添加了一个尝试失败的 SQLFiddle example，即：

SELECT a.PlaySeq, 
       a.TransMaxValue,
       IIF(ISNULL(LAG(a.TransMaxValue,1) OVER (ORDER BY a.PlaySeq), a.TransMaxValue) = a.TransMaxValue, a.TransMaxValue, LAG(a.TransMaxValue,1) OVER (ORDER BY a.PlaySeq)) AS TransMaxValueContd
FROM   myTable AS a;

编辑：感谢您的所有回答，提供了新的有用见解！
我最终使用了这个，灵感来自 answer 的 SteveC。

SELECT  a.PlaySeq, 
        a.TransMaxValue,
        (SELECT     TOP 1 x.TransMaxValue 
         FROM       myTable AS x 
         WHERE      x.PlaySeq <= a.PlaySeq 
         AND        x.TransMaxValue != 0 
         ORDER BY   x.PlaySeq DESC) AS TransMaxValueContd
FROM    myTable AS a;

Answer 1

一种简单的方法是使用 OUTER APPLY 和 SELECT TOP(1)。像这样

select m.PlaySeq, m.[TransMaxValue],
       case when m.[TransMaxValue]=0 
            then oa.TransMaxValue 
            else m.TransMaxValue end TransMaxValueContd
from myTable m
     outer apply (select top(1) mm.[TransMaxValue]
                  from myTable mm
                  where m.PlaySeq>mm.PlaySeq
                        and mm.[TransMaxValue]>0
                  order by mm.PlaySeq desc) oa;

PlaySeq TransMaxValue   TransMaxValueContd
1       250             250
2       500             500
3       0               500
4       400             400
5       0               400
6       300             300
7       500             500
8       0               500
9       0               500

Answer 2

也许这会有所帮助：

DECLARE @Tab TABLE(PlaySeq INT, TransMaxValue INT)
INSERT @Tab
VALUES(1,250),(2,500),(3,0),(4,400),(5,0)
     ,(6,300),(7,500),(8,0),(9,0)

SELECT PlaySeq, 
       TransMaxValue,
       FIRST_VALUE(TransMaxValue) OVER(PARTITION BY Grp ORDER BY PlaySeq) AS TransMaxValueContd
FROM (
      SELECT
        PlaySeq,
        TransMaxValue,
        SUM(CASE WHEN TransMaxValue = 0 THEN 0 ELSE 1 END) OVER(ORDER BY PlaySeq) AS Grp
      FROM @Tab
) AS tbl
ORDER BY PlaySeq

Answer 3

请尝试以下解决方案。

基于Windows函数ROW_NUMBER()和非等关系子句：

FROM @tbl AS t1 INNER JOIN 
            @tbl AS t2 ON t1.PlaySeq > t2.PlaySeq

SQL

-- DDL and sample data population, start
DECLARE @tbl TABLE (PlaySeq INT, TransMaxValue INT);
INSERT INTO @tbl (PlaySeq, TransMaxValue) VALUES
(1, 250),
(2, 500),
(3, 0  ),
(4, 400),
(5, 0  ),
(6, 300),
(7, 500),
(8, 0  ),
(9, 0  );
-- DDL and sample data population, end

;WITH rs AS
(
    SELECT t1.*
        , t2.TransMaxValue AS prev_value
        , ROW_NUMBER() OVER (PARTITION BY t1.PlaySeq ORDER BY t2.PlaySeq DESC) AS seq
    FROM @tbl AS t1 INNER JOIN 
        @tbl AS t2 ON t1.PlaySeq > t2.PlaySeq
    WHERE t2.TransMaxValue > 0
)
SELECT PlaySeq, TransMaxValue, TransMaxValue AS TransMaxValueContd
FROM @tbl WHERE PlaySeq = 1
UNION ALL
SELECT PlaySeq, TransMaxValue, IIF(TransMaxValue > 0, TransMaxValue, prev_value) AS TransMaxValueContd
FROM rs
WHERE seq = 1
ORDER BY PlaySeq ASC;

输出

+---------+---------------+--------------------+
| PlaySeq | TransMaxValue | TransMaxValueContd |
+---------+---------------+--------------------+
|       1 |           250 |                250 |
|       2 |           500 |                500 |
|       3 |             0 |                500 |
|       4 |           400 |                400 |
|       5 |             0 |                400 |
|       6 |           300 |                300 |
|       7 |           500 |                500 |
|       8 |             0 |                500 |
|       9 |             0 |                500 |
+---------+---------------+--------------------+

Answer 4

可能有更好的方法，但您可以尝试使用相关子查询：

SELECT q.PlaySeq, q.TransMaxValue
 , (CASE 
      WHEN q.TransMaxValue <> 0 THEN q.TransMaxValue 
      ELSE (SELECT d.TransMaxValue FROM myTable d WHERE d.PlaySeq = q.PlaySeqRef) 
    END) TransMaxValueContd
      FROM (
         SELECT PlaySeq
              , TransMaxValue
              , (SELECT MAX(PlaySeq) 
                    FROM myTable b 
                   WHERE b.PlaySeq < a.PlaySeq 
                     AND b.TransMaxValue <> 0) PlaySeqRef
             FROM myTable a) q;

查询以保留最新的非零值

4 个答案: