mysql - 在MySQL中选择某个值下的连续行

Question

选择列低于特定值的连续行

我有一个包含以下数据的表:

crashID     crash
-----------------------
1           189
2           144
3           8939        
4           748
5           988
6           102
7           392
8           482
9           185
10          101

我想选择崩溃值低于特定阈值的最长连续行。对于此示例，假设为 500。

如何在单个 MySQL 查询中执行此操作？ (v8.0.1)

期望的输出是这样的:

crashID     crash
------------------
6           102
7           392
8           482
9           185
10          101

Answer 1

您可以尝试使用间隙和孤岛方法来解决它，假设每次崩溃 lte 500 都是一个孤岛，然后找到最大的孤岛:

SET @threshold = 500;
WITH cte1 AS (
    SELECT
        crashID,
        CASE WHEN crash <= @threshold THEN 1 ELSE 0 END AS island,
        ROW_NUMBER() OVER (ORDER BY crashID) rn1,
        ROW_NUMBER() OVER (PARTITION BY CASE WHEN crash <= @threshold THEN 1 ELSE 0 END ORDER BY crashID) rn2
    FROM t
), cte2 AS (
    SELECT MIN(crashID) AS fid, MAX(crashID) AS tid
    FROM cte1
    WHERE island = 1
    GROUP BY rn1 - rn2
    ORDER BY COUNT(*) DESC
    LIMIT 1
)
SELECT *
FROM t
WHERE crashID BETWEEN (SELECT fid FROM cte2) AND (SELECT tid FROM cte2);

DB Fiddle