识别 SQLite 中缺失的序列 table

Question

我有一个 table 有 1000 条记录。每条记录代表子文件夹中的一个文件以及与该文件相关的一些属性。感兴趣的字段/列如下：

__dirpath = 包含感兴趣文件的每个子文件夹的名称 track = 文件的序列号（这些应该是连续的，范围可以从一到任何数字

我正在寻找与每个 __dirpath.

相关的文件所代表的序列中缺失的数字

列出序列中每个缺失数字的开始和结束的通用查询如下（来源：https://www.xaprb.com/blog/2005/12/06/find-missing-numbers-in-a-sequence-with-sql/）：

select start, stop from (
  select m.id + 1 as start,
    (select min(id) - 1 from sequence as x where x.id > m.id) as stop
  from sequence as m
    left outer join sequence as r on m.id = r.id - 1
  where r.id is null
) as x
where stop is not null order by start, stop;

然而，在这种情况下，我需要对与具有相同 __dirpath 值的记录相关的每个序列执行相同的操作。假设序列 table 除了通用示例中的 id 字段外还有一个 __dirpath 列，该怎么做？

这是一个带有虚拟数据的 table，并且上述查询适用于此 table，而不考虑 __dirpath：

drop table if exists sequence;
    create table sequence (__dirpath blob, id int not null);

insert into sequence(__dirpath, id) values
    ("A", 1), ("A",2), ("A", 3), ("A", 4), ("A", 6), ("A", 7), ("A", 8), ("A", 9),
    ("A", 10), ("A", 15), ("A", 16), ("A", 17), ("A", 18), ("A", 19), ("A", 20);

如果然后运行以下查询，您将获得正确的答案集：

select dir, start, stop from (
  select m.id + 1 as start,
    (select min(id) - 1 from sequence as x where x.id > m.id) as stop, m.__dirpath as dir
  from sequence as m
    left outer join sequence as r on m.id = r.id - 1
  where r.id is null
) as x
where stop is not null order by dir, start, stop;

结果正确如下：

If one then add the following records to the table:

insert into sequence(__dirpath, id) values
    ("B", 1), ("B",4), ("B", 5), ("B", 6), ("B", 7), ("B", 117), ("B", 14), ("B", 9),
    ("B", 10), ("B", 15), ("B", 16), ("B", 17), ("B", 18), ("B", 19), ("B", 20);

并重新运行上面的左外连接，结果没有意义，因为与 __dirpath = "A" 和 __dirpath = "B" 相关的值都在查询中被引用，产生：

所以问题本质上是如何修改查询以引用仅与每个 __dirpath 条目相关的记录。

Answer 1

您必须在相关子查询和连接中添加列 __dirpath：

SELECT dir, start, stop 
FROM (
  SELECT m.id + 1 start,
    (SELECT MIN(id) - 1 FROM sequence x WHERE x.__dirpath = m.__dirpath AND x.id > m.id) stop, 
     m.__dirpath dir
  FROM sequence m LEFT JOIN sequence r 
  ON m.__dirpath = r.__dirpath AND m.id = r.id - 1
  WHERE r.id IS NULL
) 
WHERE stop IS NOT NULL 
ORDER BY dir, start, stop;

另一种具有 CTE 和 window 功能的解决方案：

WITH cte AS (
  SELECT __dirpath, grp, MIN(id) min_id, MAX(id) max_id
  FROM (
    SELECT *, SUM(flag) OVER (PARTITION BY __dirpath ORDER BY id) grp
    FROM (
      SELECT *, id - 1 <> LAG(id, 1, id - 1) OVER (PARTITION BY __dirpath ORDER BY id) flag
      FROM sequence
    )
  )  
  GROUP BY __dirpath, grp
)  
SELECT c1.__dirpath, 
       MAX(c1.max_id) + 1 start,
       MIN(c2.min_id) - 1 stop
FROM cte c1 INNER JOIN cte c2
ON c2.__dirpath = c1.__dirpath AND c2.grp = c1.grp + 1
GROUP BY c1.__dirpath, c1.grp

参见demo。

识别 SQLite 中缺失的序列 table

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