Chris Pratt wrote:
> We use a transaction to prevent this. In JDBC it's very simple, just turn
> off auto-commit.
> (*Chris*)
>
Doing this may be enough, depending on the default transaction isolation level
your database runs at. To ensure that commits by others do not affect you
(even if you turn off auto-commit), you should really call:
conn.setAutoCommit(false);
conn.setTransactionIsolation(Connection.TRANSACTION_SERIALIZABLE);
at the beginning of your transaction.
Of course, if your database does not support transactions (such as MySQL), you
are stuck with the possibility of a discrepancy no matter what you do with
these calls.
Craig McClanahan
>
> ----- Original Message -----
> From: Bob Withers <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Sunday, July 04, 1999 4:33 AM
> Subject: Re: Number of rows a query retrieved?
>
> > Chris,
> >
> > It is also important to consider that it is possible for the number of
> rows
> > that will be returned to change between the two queries if other sessions
> > are updating the data base. It would be entirely possible for the select
> > count(*) to return a count of 1000 and have the second query return zero
> > rows.
> >
> > Regards,
> > Bob
> >
> > ------------------------------------------------------------------------
> > -------------------
> > Bob Withers Two things are infinite:
> the
> > universe and
> > [EMAIL PROTECTED] human stupidity, and I'm not
> sure
> > about
> > http://www.pobox.com/~bwit the universe. - Albert Einstein
> > ------------------------------------------------------------------------
> > -------------------
> > ----- BEGIN GEEK CODE BLOCK -----
> > Version 3.1 http://www.geekcode.com
> > GCS d- s: a+ C++ UO++ P L++ E--- W++ N++ o-- w++
> > O M V- PS PE Y+ PGP t+ 5 X++ r* tv+ b++ DI++ D--- G
> > e++ h--- r+++ y+++
> > ----- END GEEK CODE BLOCK -----
> >
> >
> > On Tuesday, June 29, 1999 11:35 AM, Chris Pratt
> > [SMTP:[EMAIL PROTECTED]] wrote:
> > > >From what I understand, the first query is only slightly faster than
> the
> > > second (since it doesn't have to build a full ResultSet), but Oracle has
> > > pretty aggressive caching, so the second query (having the same where
> > > clause) should run out of the cached data from the first call and be
> very
> > > quick. Overall, it's slower, but nowhere near twice as slow.
> > > (*Chris*)
> > >
> > > ----- Original Message -----
> > > From: Xizhen Wang <[EMAIL PROTECTED]>
> > > To: Chris Pratt <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
> > > Cc: <[EMAIL PROTECTED]>
> > > Sent: Monday, June 28, 1999 6:34 PM
> > > Subject: Re: Number of rows a query retrieved?
> > >
> > >
> > > >
> > > >
> > > > Chris Pratt wrote:
> > > > >
> > > > > Oh, I should have mentioned, that using simple SQL, you can also use
> > the
> > > > > COUNT operator to test how many rows will be returned. Like this:
> > > > >
> > > > > select count(*) from employees where city='San Jose'
> > > > > select * from employees where city='San Jose'
> > > >
> > > > Thank you!
> > > > So another question is: is the first query as time-comsuming as the
> 2nd
> > > > one?
> > > > if this is true, i'd rather do only one query.
> > > >
> > > > thanks!
> > > >
> > > > xizhen
> > > >
> > > >
> > > > >
> > > > > The first query will return a single row in its ResultSet that
> > consists
> > > of
> > > > > one Numeric value equal to the number of rows that the second query
> > will
> > > > > return (Assuming that no updates happen between the two
> invocations).
> > > > > (*Chris*)
> > > > >
> > > > > ----- Original Message -----
> > > > > From: Chris Pratt <[EMAIL PROTECTED]>
> > > > > To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>
> > > > > Sent: Monday, June 28, 1999 2:42 PM
> > > > > Subject: Re: Number of rows a query retrieved?
> > > > >
> > > > > > In standard JDBC, there is no way to tell this before you have
> read
> > > the
> > > > > last
> > > > > > row. There are packages, like Village or Town, that do have this
> > > > > > capability, but I have not tested them. You could also use a true
> > > OODB,
> > > > > > like CloudScape, which has this type of capability.
> > > > > > (*Chris*)
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: Xizhen Wang <[EMAIL PROTECTED]>
> > > > > > To: <[EMAIL PROTECTED]>
> > > > > > Sent: Monday, June 28, 1999 12:44 AM
> > > > > > Subject: Number of rows a query retrieved?
> > > > > >
> > > > > >
> > > > > > > Hi! In jdbc, how to know the number of rows a query retrieved?
> Is
> > > there
> > > > > > > a good way other than using ResultSet.next()?
> > > > > > >
> > > > > > > Thanks!
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > >
> >
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