如何创建由其他列分段的自动增量列

Question

我需要创建一个包含增量 id 的表，但我希望根据其他列自动对 id 进行分段。这是我想要的：

CREATE TABLE dbo.MyTable (
    myKey INT IDENTITY PRIMARY KEY,
    category INT,
    incrementalId INT
);

INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (200);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (200);

SELECT *
FROM dbo.MyTable;

我希望它显示如下内容：

myKey       category    incrementalId
----------- ----------- -------------
1           100         1
2           200         1
3           100         2
4           100         3
5           100         4
6           200         2

意思是我希望incrementalId 每个类别自动递增，并从 1 重新开始插入任何新类别。我希望在表中的任何插入上自行完成（我不想在插入此表时记住这样做）。

我认为这可以通过窗口函数和触发器来完成，但我就是不知道怎么做。

编辑：

如果发生数据删除，我希望保留数据以避免增量 ID 被转移。此外，理想情况下，在删除行的情况下不会重新给出相同的 ID（与序列或 IDENTITY 的工作方式相同）

有什么想法吗？

Answer 1

CREATE TABLE dbo.MyTable (
  myKey INT IDENTITY PRIMARY KEY,
  category INT,
  incrementalId INT
);
GO

create table dbo.nextCategoryID (
  category int,
  nextidvalue int,
  constraint PK_nextCategoryID primary key clustered( category, nextidvalue )
);
GO

create trigger numberByCategory on dbo.MyTable
after insert as 

-- Automatically add any net new category
insert into dbo.nextCategoryID ( category, nextidvalue )
    select distinct category, 1 as nextidvalue
    from inserted
    where not exists ( select * from dbo.nextCategoryID s
        where s.category = inserted.category );


-- Number the new rows in each incoming category
with numberedrows as (
    select 
        i.myKey, 
        i.category, 
        n.nextidvalue - 1 + row_number() over ( partition by i.category order by i.category ) as incrementalId
    from inserted i
    join dbo.nextCategoryID n on i.category = n.category
)
update m
    set incrementalId = n.incrementalId
from dbo.MyTable m
join inserted i on m.myKey = i.myKey
join numberedrows n on n.myKey = i.myKey;


update dbo.nextCategoryID
    set nextidvalue = 1 + ( select max( m.incrementalId ) 
        from inserted i 
        join dbo.MyTable m on i.myKey = m.myKey
        where i.category = nextCategoryID.category 
    )
where exists ( select * 
    from inserted i
    where i.category = nextCategoryID.category
);

GO

-- Test data 

INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (200);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (100);
INSERT INTO dbo.MyTable (category) VALUES (200);

insert into dbo.MyTable (category) 
values 
    ( 200 ),
    ( 200 ),
    ( 100 ),
    ( 300 ),
    ( 400 ),
    ( 400 )


SELECT *
FROM dbo.MyTable;

Answer 2

您可以通过触发器轻松实现：

CREATE TRIGGER dbo.UpdateIncrementalID
ON dbo.MyTable
AFTER  INSERT
AS 
      UPDATE x 
      SET incrementalId = ROW_NUMBER() OVER(PARTITION BY category ORDER BY myKey DESC)
      FROM dbo.MyTable x

Answer 3

我认为您不需要在表中添加额外的列“IncrementalID”。

您可以在您的选择语句中创建它。

SELECT myKey,category,ROW_NUMBER() OVER(PARTITION BY category ORDER BY myKey )incrementalId
FROM MyTable
ORDER BY myKey

样本输出。

否则，您可以从实际表创建视图。

CREATE VIEW dbo.VIEW_MyTable 
 AS
  SELECT myKey,category,ROW_NUMBER() OVER(PARTITION BY category ORDER BY myKey )incrementalId
    FROM MyTable
    ORDER BY myKey

Answer 4

您可以使用下面的更新查询来更新同一个表

;with cte as (
select mykey, category, incrementalid, row_number() over (partition by category order by mykey,category) as rn from MyTable
)
update cte
set incrementalId = rn

Answer 5

将@Kannan 的解决方案扩展为从计算列调用的 UDF：

create function dbo.fnsPartId(@mykey int)
returns int
as
begin
    declare @Ret int
    ;
    with
    enum as
    (
        select mykey, category, incrementalid, 
            row_number() over (partition by category order by mykey, category) as rn 
            from MyTable
    )
    select @Ret = rn from enum where mykey = @mykey
    return @Ret
end 

并将表格修改为：

CREATE TABLE dbo.MyTable (
    myKey INT IDENTITY PRIMARY KEY,
    category INT,
    incrementalId AS ([dbo].[fnsPartId]([mykey]))
);

Answer 6

尝试在列上创建默认约束。使用函数为该行生成下一个值作为该函数返回的默认行。

Answer 7

请试试这个（在此表上插入触发器后添加）-

create trigger InsertIncrementalID
on dbo.MyTable
after insert
as
begin
    update  mt
    set     incrementalId = (select count(mt1.category) from dbo.MyTable mt1 where mt1.category = mt.category)
    from    dbo.MyTable mt
    inner join inserted i on i.myKey = mt.myKey
end

使用触发器时请记住两点- 1.我们正在从内部触发器更新表，因此如果您在此表上有任何其他触发器（更新后），该触发器也将被执行。 2. 单选查询在该表中插入多行时，该触发器只执行一次。