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From "Lance J. Andersen" <Lance.Ander...@Sun.COM>
Subject Re: [jira] Updated: (DERBY-231) "FOR UPDATE" required for updatable result set to work
Date Fri, 04 Nov 2005 15:00:14 GMT


>Thanks for the useful infomation, but how are you inferring those cursor
>context attributes from the JDBC ResultSet being read-only?
>
>A Derby forward only ResultSet, is read only but:
>
>   - is not scrollable
>   - does not have an order by clause
>
>So it fails on two of the context items that make the SQL statement
>implicitly read only. It then comes down to is it insensitive? I always
>need to go to the JDBC tutorial book to clarify what insensitive means
>in this context and I don't have it with me until tomorrow. Though I did
>discover a post by Mamta that states Derby's forward only ResultSets are
>sensitive:
>  
>
One thing to keep in mind, while the tutorial is useful, it should not 
be used as the definitive answer, that needs to be the spec and the 
javadocs, which is part of the spec.

We have clarified and correct items in the spec which were incorrect in 
the tutorial. 

TYPE_FORWARD_ONLY ResultSets, the rows contained depend on how the 
driver and db materialize the rows.  Some drivers might materialize all 
the rows once the query is executed, others  will only be when the row 
is retrieved.

>http://mail-archives.apache.org/mod_mbox/db-derby-dev/200501.mbox/%3C41DEF292.D44626CE@Remulak.Net%3E
>
>Another way of looking at it is, what you are saying that with a
>statement like SELECT * FROM T, I can only perform a positioned update
>on it if:
>
>   - I make the JBDC ResultSet updateable
>
>   - or I add a FOR UPDATE clause to the SQL statement.
>
>Now the FOR UPDATE clause is obvious, but I can't see the link to the
>JDBC ResultSet being updateable. I can't see other databases having this
>requirement, especially as they supported positioned updates with
>read-only ResultSets before JDBC supported updateable ResultSets. I can
>see other databases being as restrictive as Derby, hence requiring the
>FOR UPDATE, but the old comment did indicate that was against the SQL
>standard.
>
>
>The patch can probably proceed without this being resolved, but it would
>be good to come to clear agreement on if SELECT * FROM T can be updated
>with a positioned update/delete and a read-only ResultSet. (Even if
>Derby doesn't support it today, it would be nice to know or not if it is
>meant to be supported).
>
>Dan.
>
>  
>

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