如何使用SQL查找具有预定义最小间隙大小的所有"间隙"

Question

我读了很多关于寻找间隙的好答案(这里，这里，这里(，但我仍然不知道如何找到最小预定义大小的间隙。

在我的案例中，空白是HE没有名字顺序的条目。

我还需要像示例中那样，从表格开头开始查找差距。

任何人都可以帮助编写一个漂亮干净的SQL语句，该语句可以简单地更改以获得预定义的最小间隙大小

预期输出示例：

+-----------+----+      +----------------+      +----------------+      +----------------+
| name      | HE |      |   GAPS >= 1    |      |   GAPS >= 2    |      |   GAPS >= 3    |
+-----------+----+      +-----------+----+      +-----------+----+      +-----------+----+
|           |  1 |      | name      | HE |      | name      | HE |      | name      | HE |
| JohnDoe01 |  2 |      +-----------+----+      +-----------+----+      +-----------+----+
| JohnDoe02 |  3 |      |           |  1 |      |           |  4 |      |           | 12 |
|           |  4 |      |           |  4 |      |           |  5 |      |           | 13 |
|           |  5 |      |           |  5 |      |           |  9 |      |           | 14 |
| JohnDoe03 |  6 |      |           |  9 |      |           | 10 |      +-----------+----+
| JohnDoe04 |  7 |      |           | 10 |      |           | 12 |
| JohnDoe05 |  8 |      |           | 12 |      |           | 13 |
|           |  9 |      |           | 13 |      |           | 14 |
|           | 10 |      |           | 14 |      +-----------+----+
| JohnDoe06 | 11 |      +-----------+----+
|           | 12 |
|           | 13 |      
|           | 14 |      
| JohnDoe07 | 15 |      
+-----------+----+

Answer 1

您可以识别间隙以及起点和终点。要识别差距，请计算非差距的数量并汇总：

select min(he), max(he), count(*) as size
from (select t.*, count(name) over (order by he) as grp
from t
) t
where name is null
group by grp;

然后，您可以使用having对特定大小的间隙进行筛选，例如2:

having count(*) >= 2

例如。

这总结了间隙，每行一个。事实上，这对我来说似乎比每行单独一行更有用。

编辑：

如果你真的想要原始的行，你可以做：

select t.*
from (select t.*,
max(he) filter (where name is not null) over (order by he) as prev_he,
min(he) filter (where name is not null) over (order by he desc) as next_he,
max(he) over () as max_he
from t
) t
where name is null and
(max(next_he, max_he + 1) - coalesce(prev_he, 0) - 1) >= 2;

编辑II:

在旧版本的MySQL/MariaDB中，您可以使用变量：

select min(he), max(he), count(*) as size
from (select t.*,
(@grp := @grp + (name is not null)) as grp
from (select t.* from t order by he) t cross join
(select @grp := 0) params
) t
where name is null
group by grp;