Обсуждение: Bulk row fetching
Hello: Do anyone know whether libpq of postgresql can support bulk row fetching, which allow multiple records to be retrieved at once during a single fetch, rather than retrieving one record at a time? Carmen _________________________________________________________________ MSN Photos is the easiest way to share and print your photos: http://photos.msn.com/support/worldwide.aspx
On Thu, Aug 15, 2002 at 02:41:57PM +0000, Carmen Wai wrote: > Hello: > > Do anyone know whether libpq of postgresql can support bulk row fetching, > which allow multiple records to be retrieved at once during a single fetch, > rather than retrieving one record at a time? Well, libpq will return a whole resultset. If that happens to contain multiple rows it gets multiple rows. Perhaps you should state more clearly what your problem is. Hope this helps, -- Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > There are 10 kinds of people in the world, those that can do binary > arithmetic and those that can't.
I want to implement a similar mechanism as bulk row fetching in MFC ODBC classes for postgresql. For the very large record sets, it can fetch the first (let say) 100 records. After that, it can automatically fetch the next 100 records WITHOUT executing the SQL statement again, it will save lots of memory resouce / time. I only find that postgresql support : select * from table_name limit N offset M, but if I do it in this way, the DB need multiple execution which will take up lots of time. Do anyone gets any idea? > > Hello: > > > > Do anyone know whether libpq of postgresql can support bulk row >fetching, > > which allow multiple records to be retrieved at once during a single >fetch, > > rather than retrieving one record at a time? > >Well, libpq will return a whole resultset. If that happens to contain >multiple rows it gets multiple rows. > >Perhaps you should state more clearly what your problem is. > >Hope this helps, > >-- >Martijn van Oosterhout <kleptog@svana.org> http://svana.org/kleptog/ > > There are 10 kinds of people in the world, those that can do binary > > arithmetic and those that can't. _________________________________________________________________ Chat with friends online, try MSN Messenger: http://messenger.msn.com
"Carmen Wai" <wai_carmen@hotmail.com> writes:
> I want to implement a similar mechanism as bulk row fetching in MFC ODBC
> classes for postgresql. For the very large record sets, it can fetch the
> first (let say) 100 records. After that, it can automatically fetch the next
> 100 records WITHOUT executing the SQL statement again, it will save lots of
> memory resouce / time.
> I only find that postgresql support : select * from table_name limit N
> offset M, but if I do it in this way, the DB need multiple execution which
> will take up lots of time.
Use a cursor.
regards, tom lane
Carmen Wai wrote: > > I want to implement a similar mechanism as bulk row fetching in MFC ODBC > classes for postgresql. For the very large record sets, it can fetch the > first (let say) 100 records. After that, it can automatically fetch the > next 100 records WITHOUT executing the SQL statement again, it will save > lots of memory resouce / time. > > I only find that postgresql support : select * from table_name limit N > offset M, but if I do it in this way, the DB need multiple execution > which will take up lots of time. > > Do anyone gets any idea? It always helps to start with the manual ;-) See: http://www.postgresql.org/idocs/index.php?libpq-example.html for an example which uses a cursor. Instead of "FETCH ALL in mycursor", you can do something like "FETCH 100 in mycursor". See: http://www.postgresql.org/idocs/index.php?sql-fetch.html for more on FETCH. See: http://www.postgresql.org/idocs/index.php?sql-declare.html for more on declaring a cursor. HTH, Joe