Обсуждение: Re: [HACKERS] Bug?
Moving to -sql. On Wed, Oct 18, 2006 at 06:53:46PM +0530, Indira Muthuswamy wrote: > Hai, > > I have encountered a problem with PostgreSQL.I have created a table > 'tab1' with a column 'a' with serial type.I entered 20 records into the > table.So the query > select max(a) from tab1; > returned 20.When I tried the same query after the command > truncate table tab1; > I found that the output of the first query as > > max > ----- > > (1 row) > When I tried to insert a new row into the table tab1 I found that the > value at column a incremented to the value 21. > But I heard from my friends that the value of the serial column gets > decremented whenever we issue the 'truncate table' command (in MS SQL > SERVER).Is the concept same with PostgreSQL or not?Can anyone clarify me on > this? Your friends are mistaken. TRUNCATE does nothing to affect sequences. -- Jim Nasby jim@nasby.net EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
See section 9.12 of the docs. On Thu, Oct 19, 2006 at 12:28:58PM +0530, Indira Muthuswamy wrote: > Then how do we clear the values of a serial column(is it done only by > dropping the column?)? > > Regards, > M.Indira > > > > On 10/19/06, Jim C. Nasby <jim@nasby.net> wrote: > > > >Moving to -sql. > > > >On Wed, Oct 18, 2006 at 06:53:46PM +0530, Indira Muthuswamy wrote: > >> Hai, > >> > >> I have encountered a problem with PostgreSQL.I have created a table > >> 'tab1' with a column 'a' with serial type.I entered 20 records into the > >> table.So the query > >> select max(a) from tab1; > >> returned 20.When I tried the same query after the command > >> truncate table tab1; > >> I found that the output of the first query as > >> > >> max > >> ----- > >> > >> (1 row) > >> When I tried to insert a new row into the table tab1 I found that the > >> value at column a incremented to the value 21. > >> But I heard from my friends that the value of the serial column gets > >> decremented whenever we issue the 'truncate table' command (in MS SQL > >> SERVER).Is the concept same with PostgreSQL or not?Can anyone clarify me > >on > >> this? > > > >Your friends are mistaken. TRUNCATE does nothing to affect sequences. > >-- > >Jim Nasby jim@nasby.net > >EnterpriseDB http://enterprisedb.com 512.569.9461 (cell) > > -- Jim Nasby jim@nasby.net EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
Then how do we clear the values of a serial column(is it done only by dropping the column?)?
Regards,
M.Indira
On 10/19/06, Jim C. Nasby <jim@nasby.net> wrote:
Moving to -sql.
On Wed, Oct 18, 2006 at 06:53:46PM +0530, Indira Muthuswamy wrote:
> Hai,
>
> I have encountered a problem with PostgreSQL.I have created a table
> 'tab1' with a column 'a' with serial type.I entered 20 records into the
> table.So the query
> select max(a) from tab1;
> returned 20.When I tried the same query after the command
> truncate table tab1;
> I found that the output of the first query as
>
> max
> -----
>
> (1 row)
> When I tried to insert a new row into the table tab1 I found that the
> value at column a incremented to the value 21.
> But I heard from my friends that the value of the serial column gets
> decremented whenever we issue the 'truncate table' command (in MS SQL
> SERVER).Is the concept same with PostgreSQL or not?Can anyone clarify me on
> this?
Your friends are mistaken. TRUNCATE does nothing to affect sequences.
--
Jim Nasby jim@nasby.net
EnterpriseDB http://enterprisedb.com 512.569.9461 (cell)
> Then how do we clear the values of a serial column(is it done only by > dropping the column?)? If you look at the following link, you will see that serial is not really a true data-type. It is merely a short-cut to get the desired results: http://www.postgresql.org/docs/8.1/interactive/datatype.html#DATATYPE-SERIAL Also, if you are interested in resetting your columns "serial" value back to 1 or 0 or -10000, you can do it using the setval() function for the following link: http://www.postgresql.org/docs/8.1/interactive/functions-sequence.html Regards, Richard Broersma Jr.