Re: nextval(), and serial updates

Hi!

In my opinion there is absolutely no doubt that this is the intended
behavior.

When you do select nextval you are saying:
INCREMENT THE COUNTER TO THE NEXT VALUE.
When you do currval, currval should (and does) give you the most up to
date value in YOUR session.

I guess that when an INSERT in a table with a sequence field is processed,
postgres will internally execute select nextval() - like a trigger.

And, also, the implementation of serial values probably assumes that you
don't call nextval yourself, unless you really know what you are doing...

Regards, Silvio

On Tue, 4 Apr 2000, Sampath, Krishna wrote:
>
> Normally, currval() points to the index sequence for the last inserted
> record.
>
> However, after I call
>     select nextval('i_seq'::text)
> on the serial data tyep i_seq, the counter gets incremented by 1. The next
> INSERT skips a number in the sequence. Is this by design? I was a bit
> surprized because the currval() gets incremented also, and you no longer
> point to the last inserted record.
>
> puzzled,
> krishna
>
> concrete example:
> create table t1 ( i serial, s varchar(20) );    -- create table
> insert into t1 (s) values ('first line');        -- insert 1 record
> select * from t1;                        -- gives (1
> row)
> select currval('t1_i_seq');                -- gives 1 as
> currval .. ok
> select nextval('t1_i_seq');                -- gives 2 as
> nextval .. ok so far
> select currval('t1_i_seq');                -- gives 2 as
> currval ... should this be 1?
> insert into t1 (s) values ('second line');    -- inserts second line,
> serial id set to 3
> select * from t1;                        -- (2 rows)
> i is now 3, should be 2
>
>
>

``````````` Silvio Emanuel Nunes Barbosa de Macedo (PhD Std) '''''''''''''
smacedo@ic.ac.uk                                         smacedo@inescn.pt
Intelligent and Interactive Systems                Telecom. and Multimedia
Imperial College, University of London                         INESC Porto
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