Question

我刚刚开始使用T-SQL的RowVersion，我注意到了一些非常有趣的东西。我创建了一个Proc以使用RowVersion列更新表，并在此proc的末尾打印出RowVersion的可读日期表示。我还添加了一个Trigger，它更新表中的数据并打印出RowVersion之前和之后。它给出了一些有趣的结果......

插入数据后从插入过程= 1900-01-01 05：43：13.373

从触发开始之前我们更改任何数据= 1900-01-01 05：43：13.377

数据发生变化后触发结束= 1900-01-01 05：43：13.377

RowVersion列的触发器值的开始已从RowVersion列的proc值的末尾更改，尽管我们还没有扩充任何数据。它也与Trigger的结尾相同。为什么是这样？它与SQL语句执行的顺序有关吗？任何帮助理解这一点将不胜感激。 proc和触发器列在下面：

CREATE PROCEDURE [dbo].[TestRowVersionProc]
AS
    INSERT INTO TestRowversion (ID, Number)
    VALUES ('6', '6')

    DECLARE @rv DATETIME 
    SELECT @rv = GenerationNumber FROM TestRowversion WHERE ID = '6'
    SELECT CONVERT(VARCHAR(50), @rv , 121)
GO


CREATE TRIGGER [dbo].[TestRowversion_AfterInsertUpdate] ON [dbo].[TestRowversion] AFTER INSERT,UPDATE
AS
    if @@rowcount = 0 return
    set nocount on

    DECLARE @rv DATETIME 
    SELECT @rv = GenerationNumber FROM TestRowversion WHERE ID = '6'
    SELECT CONVERT(VARCHAR(50), @rv , 121)

    DECLARE @Id NVARCHAR(1) 
    SELECT @Id = ID FROM inserted

    UPDATE TestRowversion
    SET Number = 'FromTrigger'
    WHERE ID = '6'

    SELECT @rv = GenerationNumber FROM TestRowversion WHERE ID = '6'
    SELECT CONVERT(VARCHAR(50), @rv , 121)

GO

Answer 1

https://docs.microsoft.com/en-us/sql/t-sql/data-types/rowversion-transact-sql

rowversion数据类型只是一个递增的数字，不会保留日期或时间。
每个数据库都有一个计数器，该计数器针对在数据库中包含rowversion列的表上执行的每个插入或更新操作递增。此计数器是数据库rowversion。这会跟踪数据库中的相对时间，而不是可以与时钟关联的实际时间。
DATETIME准确度舍入为.000，.003或.007秒的增量

Answer 2

执行顺序是，使用一些实际的时间戳值：

| Event time                | Event time                  | RowVersion |
|---------------------------|-----------------------------|------------|
| Start of trigger          | 2017-12-05 10:50:26.8506034 | 28,804,001 |
|  End  of trigger          | 2017-12-05 10:50:26.8506034 | 28,804,002 |
| After insert              | 2017-12-05 10:50:26.8662212 | 28,804,002 |

您可以将rowversion转换为人类可读的形式：

SELECT CAST(GenerationNumber AS bigint) FROM TestRowVersion --timestamp is an 8-byte (64-bit) integer

你订购的心理模型是错误的。

表：

CREATE TABLE TestRowVersion (
    ID varchar(50), 
    Number varchar(50),
    GenerationNumber timestamp
)

插入程序：

ALTER PROCEDURE [dbo].[TestRowVersionProc]
AS
    INSERT INTO TestRowversion (ID, Number)
    VALUES ('6', '6')

    DECLARE @rv bigint
    SELECT @rv = CAST(GenerationNumber AS bigint) FROM TestRowversion WHERE ID = '6'
    SELECT CAST(SYSDATETIME() AS varchar(50))+' After insert    '+CAST(@rv AS varchar(50))
GO

<强>触发：

CREATE TRIGGER [dbo].[TestRowversion_AfterInsertUpdate] ON [dbo].[TestRowversion] AFTER INSERT,UPDATE
AS
    if @@rowcount = 0 return
    set nocount on

    DECLARE @rv bigint
    SELECT @rv = CAST(GenerationNumber AS bigint) FROM TestRowversion WHERE ID = '6'
    SELECT CAST(SYSDATETIME() AS varchar(50))+' Start of trigger    '+CAST(@rv AS varchar(50))

    DECLARE @Id NVARCHAR(1) 
    SELECT @Id = ID FROM inserted

    UPDATE TestRowversion
    SET Number = 'FromTrigger'
    WHERE ID = '6'

    SELECT @rv = CAST(GenerationNumber AS bigint) FROM TestRowversion WHERE ID = '6'
    SELECT CAST(SYSDATETIME() AS varchar(50))+' End of trigger  '+CAST(@rv AS varchar(50))

SQL RowVersion在触发器中增加数据之前递增

2 个答案: