Question on SQL Update behaviour

I have a question on how SQL Server updates records. Say assuming if I have
a table with 50000 records.. and i need to update a particular field C in
this table, based on field A and field B on the same table. I can either
write a set based SP or a cursor based SP to do that.
If I update it using cursors, I can see the records being updated 1 by 1. If
I update the whole thing using a set based SP, am I right to say that I will
not see any records updated till the process is over? Does SQL Server does
the transaction commitment itself if I write it using the set-based
approach?
Thanks.
Hi,
Update with set will do a batch updat based on the condition you are gving
in the where clause. So until the transaction is commited
you will not be able to see change. Where as Cursor does a row by row
operation. So after each record update you could see the
change.
Have a look into ISOLATION LEVEL topic in books online.
Thanks
Hari
SQL Server MVP
"Nestor" <n3570r@.yahoo.com> wrote in message
news:uncViVfgFHA.2904@.tk2msftngp13.phx.gbl...
>I have a question on how SQL Server updates records. Say assuming if I have
>a table with 50000 records.. and i need to update a particular field C in
>this table, based on field A and field B on the same table. I can either
>write a set based SP or a cursor based SP to do that.
> If I update it using cursors, I can see the records being updated 1 by 1.
> If I update the whole thing using a set based SP, am I right to say that I
> will not see any records updated till the process is over? Does SQL Server
> does the transaction commitment itself if I write it using the set-based
> approach?
> Thanks.
>
|||thanks for the prompt response... i'm really curious about how the table
will be locked up since i'm updating the table based on conditions from
fields that are in the same table as well...
will cursors work better in this case than batch insert due to the lockups?
"Hari Prasad" <hari_prasad_k@.hotmail.com> wrote in message
news:uGQThcfgFHA.576@.TK2MSFTNGP15.phx.gbl...
> Hi,
> Update with set will do a batch updat based on the condition you are gving
> in the where clause. So until the transaction is commited
> you will not be able to see change. Where as Cursor does a row by row
> operation. So after each record update you could see the
> change.
> Have a look into ISOLATION LEVEL topic in books online.
> Thanks
> Hari
> SQL Server MVP
> "Nestor" <n3570r@.yahoo.com> wrote in message
> news:uncViVfgFHA.2904@.tk2msftngp13.phx.gbl...
>
|||you can actually see the changes taking place by running a query with the
table hint nolock as in: select count(*) from mytable with (nolock) where...
I use this approach at times to see how far in a large insert or update is so
I can calculate how much longer the statement will take.
regards,
Mark Baekdal
http://www.dbghost.com
http://www.innovartis.co.uk
+44 (0)208 241 1762
Build, Comparison and Synchronization from Source Control = Database change
management for SQL Server
"Nestor" wrote:

> thanks for the prompt response... i'm really curious about how the table
> will be locked up since i'm updating the table based on conditions from
> fields that are in the same table as well...
> will cursors work better in this case than batch insert due to the lockups?
>
>
> "Hari Prasad" <hari_prasad_k@.hotmail.com> wrote in message
> news:uGQThcfgFHA.576@.TK2MSFTNGP15.phx.gbl...
>
>