如何解决根据当前值按顺序返回上一个和下一个值
我有下表：
CREATE TABLE [opTest]
(
[name] varchar(50),[task] varchar(50),[desc] varchar(100),[seq] varchar(5)
)
INSERT INTO [opTest] VALUES
('Yale','Paint','Prime Part','100'),('Yale','Paint Part','200'),'Assembly','Front Wheel Assembly','Rear Wheel Assembly','Chain Assembly','300'),'HUB Assembly','400'),'Final Assembly','500'),'CNC inspection','CNC Machine inspection','100')
+------+----------------+------------------------+-----+
| name | task | desc | seq |
+------+----------------+------------------------+-----+
| Yale | Paint | Prime Part | 100 |
| Yale | Paint | Paint Part | 200 |
| Yale | Assembly | Front Wheel Assembly | 100 |
| Yale | Assembly | Rear Wheel Assembly | 200 |
| Yale | Assembly | Chain Assembly | 300 |
| Yale | Assembly | HUB Assembly | 400 |
| Yale | Assembly | Final Assembly | 500 |
| Yale | CNC inspection | CNC Machine inspection | 100 |
+------+----------------+------------------------+-----+
我想按顺序输出具有上一个、当前和下一个任务的数据。我希望它看起来像这样：
+------+----------------+------------------------+-----------+-----------+-----------+
| Name | Task | Description | Prev Task | Curr Task | Next Task |
+------+----------------+------------------------+-----------+-----------+-----------+
| Yale | Assembly | Front Wheel Assembly | NULL | 100 | 200 |
| Yale | Assembly | Rear Wheel Assembly | 100 | 200 | 300 |
| Yale | Assembly | Chain Assembly | 200 | 300 | 400 |
| Yale | Assembly | HUB Assembly | 300 | 400 | 500 |
| Yale | Assembly | Final Assembly | 400 | 500 | NULL |
| Yale | CNC inspection | CNC Machine inspection | NULL | 100 | NULL |
| Yale | Paint | Prime Part | NULL | 100 | 200 |
| Yale | Paint | Paint Part | 100 | 200 | NULL |
+------+----------------+------------------------+-----------+-----------+-----------+
我正在使用以下查询，但不知道为什么它不起作用。我用单个字段表做了一个简单的测试，它奏效了。唯一的区别是该字段在我的测试中是 int，但我正在转换为 int，所以应该没有问题。
SELECT
[Name] AS [Name],[Task] AS [Task],[Desc] AS [Description],(SELECT TOP(1) t1.[Seq]
FROM [opTest] t1
WHERE CAST(t1.[Seq] AS int) > CAST([Seq] AS int)
ORDER BY t1.[Seq] ASC) AS [Prev Task],[Seq] AS [Curr Task],(SELECT TOP(1) t1.[Seq]
FROM [opTest] t1
WHERE CAST(t1.[Seq] AS int) < CAST([Seq] AS int)
ORDER BY t1.[Seq] DESC) AS [Next Task]
FROM
[opTest]
ORDER BY
[Name] ASC,[Task] ASC,[Seq] ASC
返回这个结果：
+------+----------------+------------------------+-----------+-----------+-----------+
| Name | Task | Description | Prev Task | Curr Task | Next Task |
+------+----------------+------------------------+-----------+-----------+-----------+
| Yale | Assembly | Front Wheel Assembly | NULL | 100 | NULL |
| Yale | Assembly | Rear Wheel Assembly | NULL | 200 | NULL |
| Yale | Assembly | Chain Assembly | NULL | 300 | NULL |
| Yale | Assembly | HUB Assembly | NULL | 400 | NULL |
| Yale | Assembly | Final Assembly | NULL | 500 | NULL |
| Yale | CNC inspection | CNC Machine inspection | NULL | 100 | NULL |
| Yale | Paint | Prime Part | NULL | 100 | NULL |
| Yale | Paint | Paint Part | NULL | 200 | NULL |
+------+----------------+------------------------+-----------+-----------+-----------+
解决方法
在您的查询中，您应该使用表别名并在所有列名前加上别名。
您的问题是您没有为第二列 [Seq] 指定别名。是来自 t1 还是 [opTest] ？ SQL Server 假定它来自 t1
CAST(t1.[Seq] AS int)
> CAST([Seq] AS int) -- this is from which table ?
要修复您的查询，请向该列添加适当的别名。例如。T.[Seq]
SELECT
[Name] AS [Name],[Task] AS [Task],[Desc] AS [Description],( SELECT TOP(1) t1.[Seq] FROM [opTest] t1
WHERE CAST(t1.[Seq] AS int) > CAST(T.[Seq] AS int)
ORDER BY t1.[Seq] ASC )
AS [Prev Task],[Seq] AS [Curr Task],( SELECT TOP(1) t1.[Seq] FROM [opTest] t1
WHERE CAST(t1.[Seq] AS int) < CAST(T.[Seq] AS int)
ORDER BY t1.[Seq] DESC )
AS [Next Task]
FROM [opTest] T
ORDER BY [Name] ASC,[Task] ASC,[Seq] ASC
您可以使用 LEAD() 或 LAG() 并避免使用子查询
我看到两个问题。
首先，在两个子查询中，您将字段 [seq] 与其自身进行比较。您必须在两个 [seq] 提及的子查询中明确说明您要比较的查询级别。当不明确时，它只是默认为当前级别。
其次，您只过滤两个子查询中的 [seq]。这意味着它将显示它的上一个或下一个值，而不管它是否与 [task] 实际相关。
另外，就像之前的答案提到的那样。为什么不直接使用 LEAD 和 LAG 函数？
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