如何在SQL中的组内按顺序查找缺失值？

Question

我有一张身份证和职位表

CREATE TABLE #MissingSequence (ID INT NOT NULL, Position INT NOT NULL)
INSERT INTO #MissingSequence (ID,Position)
SELECT 36,1
UNION ALL SELECT 36,2
UNION ALL SELECT 36,3
UNION ALL SELECT 36,4
UNION ALL SELECT 36,5
UNION ALL SELECT 36,6
UNION ALL SELECT 44,1
UNION ALL SELECT 44,3
UNION ALL SELECT 44,4
UNION ALL SELECT 44,5
UNION ALL SELECT 44,6

我想要找到的是,如果在ID的位置序列中有任何中断,在这种情况下,在44和44,3之间的中断

我成功地解析了:

SELECT  l.ID
    ,Start_Position = MIN(l.Position) + 1
    ,Stop_Position = MIN(fr.Position) - 1
FROM #MissingSequence l
LEFT JOIN #MissingSequence r 
    ON l.Position = r.Position - 1
LEFT JOIN #MissingSequence fr 
    ON l.Position < fr.Position
WHERE r.Position IS NULL
    AND fr.Position IS NOT NULL
GROUP BY l.ID

但如果有多个ID值,则无效.如果只存在一个ID,则它可以工作.

想法,意见,建议？

谢谢!

Answer 1

左边的自我加入是一种很好的直觉,但我不认为聚合会削减它,当然你需要在自连接中包含匹配ID子句.

这是一个(ANSI兼容的)版本,使用null-left-join的想法,选择一个顶行和一个底行并检查它们之间没有任何内容:

SELECT
    above.ID AS ID, below.Position+1 AS Start_Position, above.Position-1 AS End_Position
FROM MissingSequence AS above
JOIN MissingSequence AS below
    ON below.ID=above.ID AND below.Position<above.Position-1
LEFT JOIN MissingSequence AS inbetween
    ON inbetween.ID=below.ID AND inbetween.Position BETWEEN below.Position+1 AND above.Position-1
WHERE inbetween.ID IS NULL;

+----+----------------+--------------+
| ID | Start_Position | End_Position |
+----+----------------+--------------+
| 44 |              2 |            2 | 
+----+----------------+--------------+