Обсуждение: SERIAL problems?

Hi,

I just saw these in the TODO list:

o %Disallow changing DEFAULT expression of a SERIAL column?   This should be done only if the existing SERIAL problems
cannotbe 
 
fixed.
o %Disallow ALTER SEQUENCE changes for SERIAL sequences   because pg_dump does not dump the changes

What are the "existing problems"?

I am asking because I am experimenting to implement
the SQL2003 compliant form for the serial type
to be able specify the underlying sequence
parameters:

SERIAL [ GENERATED  [ ALWAYS | BY DEFAULT ] AS IDENTITY (   [ INCREMENT [ BY ] increment ]   [ MINVALUE minvalue | NO
MINVALUE]   [ MAXVALUE maxvalue | NO MAXVALUE ]   [ START [ WITH ] start ]   [ CACHE cache ]   [ [ NO ] CYCLE ] ) ]
 

Best regards,
Zoltán Böszörményi

Zoltan Boszormenyi <zboszor@dunaweb.hu> writes:
> What are the "existing problems"?

Please read the archives; this has been discussed recently.
There's a lot of disagreement about what ALTER should allow
and what pg_dump should do with an altered sequence.

> I am asking because I am experimenting to implement
> the SQL2003 compliant form for the serial type
> to be able specify the underlying sequence
> parameters:

Be aware that the big problem with SQL2003 is that it expects an
"action at a distance" behavior whereby different references to a
generator all return the same result if executed within the same
query cycle.  This makes the construct not equivalent to either
nextval() or currval(), but some hybrid with hidden state; and
changing of that state would have to tie into core parts of the
executor.  It looks pretty messy :-(
        regards, tom lane