Q:用于在数据中查找孤岛的SQLite查询(即，值满足特定阈值的连续行)

Question

我有一个SQLite数据库，其中包含一段时间内在癌症有机体中发现的死亡细胞的百分比(注意:为了可读性，时间列值被更改为简单的数字)。

id  time                deadcellspercent
1   000000001000000000  35
2   000000002000000000  54
3   000000003000000000  31
4   000000004000000000  15
5   000000005000000000  38
6   000000006000000000  70
7   000000007000000000  28
8   000000008000000000  13
9   000000009000000000  99
10  000000010000000000  51

我想创建一个SQLite查询，它将返回百分比低于某个阈值数字的时间范围。例如，如果我说我希望阈值是>= 20，那么查询结果应该返回：

ts_start            ts_end
000000001000000000  000000003000000000
000000005000000000  000000007000000000
000000009000000000  000000010000000000

我如何构造查询来实现这一点呢？我读过诸如"SQLite“、"gaps and islands”和"analytic functions“之类的主题，但我是SQLite新手，无法理解它们以获得所需的结果。

任何帮助都将不胜感激。

Answer 1

有了窗口函数、空隙和孤岛，您就走上了正确的道路。

首先，让我们使用您的示例数据并用它填充一个表：

CREATE TABLE cells(id INTEGER PRIMARY KEY, time TEXT, deadcellspercent INTEGER);
INSERT INTO cells VALUES(1,'000000001000000000',35);
INSERT INTO cells VALUES(2,'000000002000000000',54);
INSERT INTO cells VALUES(3,'000000003000000000',31);
INSERT INTO cells VALUES(4,'000000004000000000',15);
INSERT INTO cells VALUES(5,'000000005000000000',38);
INSERT INTO cells VALUES(6,'000000006000000000',70);
INSERT INTO cells VALUES(7,'000000007000000000',28);
INSERT INTO cells VALUES(8,'000000008000000000',13);
INSERT INTO cells VALUES(9,'000000009000000000',99);
INSERT INTO cells VALUES(10,'000000010000000000',51);

一种可能的查询(它使用窗口函数，因此需要sqlite - 3.25或更高版本的最新版本)：

WITH islands AS (SELECT id, time
                      , row_number() OVER w1 - row_number() OVER w2 AS diff
                      , deadcellspercent >= 20 AS wanted
                 FROM cells
                 WINDOW w1 AS (ORDER BY time)
                      , w2 AS (PARTITION BY deadcellspercent >= 20 ORDER BY time))
SELECT min(time) AS ts_start, max(time) AS ts_end
FROM islands
WHERE wanted = 1
GROUP BY diff
ORDER BY diff;

产生：

ts_start            ts_end            
------------------  ------------------
000000001000000000  000000003000000000
000000005000000000  000000007000000000
000000009000000000  000000010000000000

(在DBA stackexchange上受到this post的严重影响；请参考它以获得解释)。