每年的标识符

Question

我想要每年都有一个单调递增的标识符，每年从 1 开始。 BusinessKey 列中可能存在 NULL 行。我将在 INSERT 触发器中调用该函数：

DROP TABLE IF EXISTS [dbo].[Test];

CREATE TABLE [dbo].[Test] (
  [Id] [int] IDENTITY(1, 1) PRIMARY KEY CLUSTERED,
  [Year] [int] NOT NULL,
  [BusinessKey] [int]
)
GO

INSERT INTO [dbo].[Test]([Year], [BusinessKey]) VALUES
(2024, 1),
(2024, 2),
(2024, 3),
(2024, NULL),
(2024, NULL),
(2025, 1),
(2025, 2),
(2025, NULL);

-- Make a hole (gap) in the id column
DELETE FROM [dbo].[Test] WHERE [Id] = 2
GO

SELECT
  *,
  ROW_NUMBER() OVER (PARTITION BY [Year] ORDER BY [Id]) AS BuisnessKeyCalculated
FROM [dbo].[Test]

这给出了：

身份证	年份	业务密钥	业务密钥已计算	预计
1	2024	1	1	1
3	2024	3	2	3
4	2024	空	3	4
5	2024	空	4	5
6	2025	1	1	1
7	2025	2	2	2
8	2025	空	3	3

有人知道如何用窗口函数解决这个问题吗？

Answer 1

以下似乎产生了预期的结果：

select *, coalesce(
  businesskey,
  count(case when businesskey is null then 1 end) over (partition by year order by businesskey, id) + 
  max(businesskey) over (partition by year)
) as expected
from t

count() over ()

技巧将增加的行号分配给空值。

max() over ()

调整这些行号。