与PostgreSQL相同的timestamp / rowversion（SQL Server）是什么

Question

Could someone help me find the equivalent of Timestamp/Rowversion (SQL Server) with PostgreSQL?

I'm using NHibernate on Mono (UNIX).

I think that Timestamp (PostgreSQL) is the equivalent of Datetime (SQL Server) - it's not what I'm looking for .

Edit 1: For those who don't know what is a Timestamp/Rowversion in SQL Server: http://msdn.microsoft.com/en-us/library/ms182776.aspx (It is mostly used for optimistic concurrency)

Answer 1

See the system columns section in PostgreSQL documentation. In particular, xmin might be what you're looking for.

But be careful using any system columns. They are by definition implementation specific and the details of some of them might change with future versions.

Answer 2

If I understand correctly rowversion is the same as serial ? If not - you'd have to make your own with triggers.

Answer 3

You can create it manually:

1. Create sequence
2. Create trigger for insert and update for each table that contains rowversion column
3. Set rowversion column from sequence

Answer 4

The key thing being missed is that rowversion type changed each time there is an update to the row, even if the net result is that, the row is not changed.

CREATE TABLE MyTest (myKey int PRIMARY KEY  
    ,myValue int, RV rowversion);  
GO   
INSERT INTO MyTest (myKey, myValue) VALUES (1, 0);  
GO   
INSERT INTO MyTest (myKey, myValue) VALUES (2, 0);  
GO  

select * from MyTest
Go

update MyTest set myValue = 0 
go

/* row version will have changed */
select * from MyTest
Go

The only choice I have found is to create an update trigger.