sql - 如何选择行和附近的行

Question

SQL Fiddle

背景

我有一个需要注意的值表:

| 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，并且我想选择它周围的行。在此示例问题中，只要说出 ID 为 ±3 的行就足够了。这意味着我想要:

| 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  | ─╯

Note: In reality it's a table of 9M rows, and 15k need attention.

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:

• 总行数为 900 万行
• 15,000 个有趣行
• 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

这是使用移动最大值重写的现有逻辑:

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