Question

背景

我有一些需要注意的值表：

| ID      | AddedDate   |
|---------|-------------|
|       1 | 2010-04-01  |
|       2 | 2010-04-01  |
|       3 | 2010-04-02  |
|       4 | 2010-04-02  |
|       5 | NULL        | <----------- needs attention
|       6 | 2010-04-02  |
|       7 | 2010-04-03  |
|       8 | 2010-04-04  |
|       9 | 2010-04-04  |
| 2432659 | 2016-06-15  |
| 2432650 | 2016-06-16  |
| 2432651 | 2016-06-17  |
| 2432672 | 2016-06-18  |
| 2432673 | NULL        | <----------- needs attention
| 2432674 | 2016-06-20  |
| 2432685 | 2016-06-21  |

我想选择AddedDate为空的行，我想选择它周围的行。在这个示例问题中，说ID为±3的行就足够了。这意味着我想：

| ID      | AddedDate   |
|---------|-------------|
|       2 | 2010-04-01  | ─╮
|       3 | 2010-04-02  |  │
|       4 | 2010-04-02  |  │
|       5 | NULL        |  ├──ID values ±3
|       6 | 2010-04-02  |  │
|       7 | 2010-04-03  |  │
|       8 | 2010-04-04  | ─╯

| 2432672 | 2016-06-18  | ─╮
| 2432673 | NULL        |  ├──ID values ±3
| 2432674 | 2016-06-20  | ─╯

注意：实际上它是一个9M行的表，需要注意15k。

尝试

首先，我创建一个查询来构建我有兴趣返回的范围：

SELECT
  ID-3 AS [Low ID],
  ID+3 AS [High ID]
FROM Items
WHERE AddedDate IS NULL

Low ID   High ID
-------  -------
2        8 
2432670  2432676

所以我最初尝试使用它确实有效：

WITH dt AS (
   SELECT ID-3 AS Low, ID+3 AS High
   FROM Items
   WHERE AddedDate IS NULL
)
SELECT * FROM Items
WHERE EXISTS(
    SELECT 1 FROM dt
    WHERE Items.ID BETWEEN dt.Low AND dt.High)

但是当我在真实数据上尝试时：

总行数900万
15,000 有趣的行
子树成本为63,318,400
需要几个小时（在我放弃并取消之前）

可能有一种更有效的方法。

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Answer 1

这是您使用移动max：

重写的现有逻辑

WITH dt AS (
   SELECT
      ID, AddedDate,
      -- check if there's a NULL within a range of +/- 3 rows
      -- and remember it's ID 
      max(case when AddedDate is null then id end)
      over (order by id 
            rows between 3 preceding and 3 following) as NullID
   FROM Items 
)
SELECT *
FROM dt
where id between NullID-3 and NullID+3

Answer 2

以下是使用窗口子句的一种方法：

select i.*
from (select i.*,
             count(*) over (order by id rows between 3 preceding and 1 preceding) as cnt_prec,
             count(*) over (order by id rows between 1 following and 3 following) as cnt_foll,
             count(addeddate) over (order by id rows between 3 preceding and 1 preceding) as cnt_ad_prec,
             count(addeddate) over (order by id rows between 1 following and 3 following) as cnt_ad_foll
      from items
     ) i
where cnt_ad_prec <> cnt_prec or
      cnt_ad_foll <> cnt_foll or
      addeddate is null;
order by id;

这将返回列中NULL或NULL的三行内的所有行。

与计数进行比较的必要性是避免最小和最大ID上的边缘问题。

Answer 3

另一种方式：

SELECT i1.*
    FROM Items i1, Items i2
        WHERE i2.AddedDate IS NULL AND ABS(i1.ID - i2.ID) <= 3

我希望AddedDate列上有索引。

Answer 4

尝试与其他答案不同的方法...如何使用表变量来存储您想要的ID。然后你加入。我希望插件执行得足够快，然后SELECT可以利用Items中的聚簇索引。不幸的是，我没有你的数据来测试它的效率：

DECLARE @userData TABLE(
    idInRange int NOT NULL
)

INSERT INTO @userData (idInRange)
SELECT DISTINCT i.Id + r 
FROM Items i 
CROSS JOIN (
  SELECT -3 as r UNION ALL SELECT -2 as r UNION ALL SELECT -1 as r UNION ALL SELECT 0 as r UNION ALL
  SELECT 1 as r UNION ALL SELECT 2 as r UNION ALL SELECT 3 as r 
) yourRange
WHERE AddedDate IS NULL;

SELECT i.*
FROM @userData u
INNER JOIN Items i ON i.ID = u.idInRange

编辑在填充表变量时添加DISTINCT，以避免重复的行，以防万一有两个连续的NULL日期并且它们的id范围重叠

如何选择行和附近的行

背景

尝试

奖金阅读

4 个答案: