Re: jdbc question
From: Thomas Kellerer (NNGNVRDSJEBN_at_spammotel.com)
Date: 12/30/04
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Date: Thu, 30 Dec 2004 17:22:41 +0100
Sudsy wrote on 30.12.2004 15:05:
>> Why not do it the other way round? Update the row first, then check
>> the number of affected rows (which is returned by the executeUpdate()
>> method and is DBMS indepdent). If zero records were affected then the
>> record is not there and you can insert it. Thus you do not need to
>> rely on error codes for specific DBMS when catching an error during
>> the insert.
>
>
> I was wondering if/when someone would make this suggestion! The problem
> is, as others have mentioned, a matter of timing. Suppose you try an
> update and it fails. Between that point in time and the time you try an
> insert, another database client inserts a record with the same primary
> key. So now your insert fails and you have to fallback to performing
> the update again. KISS and perform an insert; iff it fails then try to
> update.
Without specific requirements there is no way telling which version is
better. If this is e.g. a data load that is performed during the night, the
the solution is absolutely valid. If this is a use case with highly
partioned data (each user edits different records) then it's valid as well,
if the situation is a highly dynamic entry system where the situation that
you sketched is very likely to happen, then obviously this is not a good
idea. On the other hand: if you expect more updates then inserts to be
successful, the overall performance would be *much* better this way because
the index lookup for the primary key is only needed once for the update but
twice for the inser/update combo.
I was simply offering a different solution. If it's feasible for the
situation of the OP is up to him (and he did not give information to us in
order to judge that)
Thomas
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