在数据透视查询中查找最后一个"非空"值

Question

我有以下查询:

 SELECT * FROM 
                (
                    SELECT unix_timestamp, input_raw, tag_id 
                    from [200030].[dbo].inputs
                    WHERE inputs.date_time > dateadd(day,-1,getdate())
                    AND
                    (tag_id = 92164 or tag_id = 92149)
                ) src
                pivot
                (
                    max(input_raw)
                    FOR tag_id IN ([92164], [92149])
                ) piv
                ORDER by unix_timestamp DESC

这很棒,很有效.它给了我结果:

但是,我希望查询为我做一件事.

每当存在'NULL'结果时,我希望查询将'NULL'替换为列中的最后一个'non-NULL'值.

例如,列'92164'中看到的第一个NULL将替换为'211'.

此外,有可能会有几个'NULL'是一行,所以查询需要继续上升,直到找到无NULL.

我已经能够用PHP实现这一目标.将结果放入2D关联数组并运行找到空值的函数然后循环查找最后一个非NULL,但我真的想在SQL中尽可能地执行此操作.我更愿意使用

while( $row = sqlsrv_fetch_array( $stmt, SQLSRV_FETCH_ASSOC)){
  //code     
}

方法比分配几个数组.

有帮助吗？

谢谢

//编辑

忘记添加,这仅适用于空值以上的任何非空值.例如,如果第一行为NULL,则可以接受.

Answer 1

您可以将数据透视查询放入 CTE 中，并在确定要显示的值时重复使用 CTE。您的数据仅在第一列中具有空值，但这里是处理两列中的空值的版本。

WITH C AS
(
  SELECT * 
  FROM (
       SELECT unix_timestamp, input_raw, tag_id 
       FROM inputs
       WHERE date_time > dateadd(day,-1,getdate()) AND
             (tag_id = 92164 OR tag_id = 92149)
       ) src
  PIVOT
       (
       MAX(input_raw)
       FOR tag_id IN ([92164], [92149])
       ) piv
)
SELECT C1.unix_timestamp,
       (
       SELECT TOP(1) C2.[92164] 
       FROM C AS C2
       WHERE C1.unix_timestamp <= C2.unix_timestamp AND
             C2.[92164] IS NOT NULL
       ORDER BY C2.unix_timestamp
       ) AS [92164],
       (
       SELECT TOP(1) C2.[92149] 
       FROM C AS C2
       WHERE C1.unix_timestamp <= C2.unix_timestamp AND
             C2.[92149] IS NOT NULL
       ORDER BY C2.unix_timestamp
       ) AS [92149] 
FROM C AS C1
ORDER by C1.unix_timestamp DESC;

如果您遇到性能问题，将 CTE 的结果存储在具有有用的聚集键索引的临时表中可能会更快。

CREATE TABLE #C
(
  unix_timestamp int PRIMARY KEY,
  [92164] int,
  [92149] int
);

INSERT INTO #C
SELECT *
FROM (
      SELECT unix_timestamp, input_raw, tag_id 
      FROM inputs
      WHERE date_time > dateadd(day,-1,getdate()) AND
            (tag_id = 92164 OR tag_id = 92149)
      ) src
PIVOT
      (
      MAX(input_raw)
      FOR tag_id IN ([92164], [92149])
      ) piv;

SELECT C1.unix_timestamp,
       (
       SELECT TOP(1) C2.[92164] 
       FROM #C AS C2
       WHERE C1.unix_timestamp <= C2.unix_timestamp AND
             C2.[92164] IS NOT NULL
       ORDER BY C2.unix_timestamp
       ) AS [92164],
       (
       SELECT TOP(1) C2.[92149] 
       FROM #C AS C2
       WHERE C1.unix_timestamp <= C2.unix_timestamp AND
             C2.[92149] IS NOT NULL
       ORDER BY C2.unix_timestamp
       ) AS [92149]
FROM #C AS C1
ORDER by C1.unix_timestamp DESC;

DROP TABLE #C;