Обсуждение: now() does not change within a transaction

Hi pgsql-sql list, 
I did some testing around tables using a column 
timestamp with time zone not null default now(). 
I have noticed a valuable feature: 
As long as being inside a transaction initiated by 
begin; 
the return value of the now() function does not change. 
Is this intended - as written in the documentation? 
Can I rely on it, so future releases of PostgreSQL 
will act the same. 
Regards, Christoph 

On Thu, Apr 18, 2002 at 02:04:35PM +0000, Christoph Haller wrote:
> Hi pgsql-sql list, 
> I did some testing around tables using a column 
> timestamp with time zone not null default now(). 
> I have noticed a valuable feature: 
> As long as being inside a transaction initiated by 
> begin; 
> the return value of the now() function does not change. 
> Is this intended - as written in the documentation? 
Sure. See (for example):

http://docs.linux.cz/PostgreSQL/functions-datetime.html#FUNCTIONS-DATETIME-CURRENT 
  It is quite important to realize that CURRENT_TIMESTAMP and related  functions all return the time as of the start of
thecurrent transaction;  their values do not increment while a transaction is running. But  timeofday() returns the
actualcurrent time.
 
test=# select timeofday()::timestamp;          timeofday
-------------------------------2002-04-18 14:39:36.459162+02
       Karel

-- Karel Zak  <zakkr@zf.jcu.cz>http://home.zf.jcu.cz/~zakkr/C, PostgreSQL, PHP, WWW, http://docs.linux.cz,
http://mape.jcu.cz

Christoph Haller wrote:
> Hi pgsql-sql list, 
> I did some testing around tables using a column 
> timestamp with time zone not null default now(). 
> I have noticed a valuable feature: 
> As long as being inside a transaction initiated by 
> begin; 
> the return value of the now() function does not change. 
> Is this intended - as written in the documentation? 
> Can I rely on it, so future releases of PostgreSQL 
> will act the same. 

Yes, this is intended and will not change.

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