Is there an equivalent of rowversion in SQL Server

问题:

I am looking for something similar to rowversion but for the whole table : a unique number automatically generated that can be used to know if table has changed.

Eg :

SELECT TABLE_VERSION('FOO')
0x00000000000007D2

INSERT INTO FOO (...) VALUES (1, 'Hello world')

SELECT TABLE_VERSION('FOO')
0x00000000000007D5

Does it exists in SQL Server ?

If not, is there any alternative ? Somethings that allow to track changes on a column would be great too. I have been thinking of using HASHBYTES, but unfortunately it only gives hash for a single column value not for the whole column.

回答1:

There is not such a thing in SQL Server, however you can implement it easly with triggers. I have used it to assist cache invalidation for web apps.

first create the table etags:

CREATE TABLE etags
(
   etag_name varchar(128) NOT NULL PRIMARY KEY,
   etag_value uniqueidentifier NOT NULL
)

Insert a value for the Foo table:

INSERT INTO etags VALUES ('foo', NEWID())

Then create a trigger for the foo table that updates the etag value when table changes

CREATE TRIGGER foo_etag
ON foo FOR INSERT, UPDATE, DELETE
AS
  SET NOCOUNT ON
  UPDATE etags SET etag_value = NEWID()
  WHERE etag_name = 'Foo'