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Date: Fri, 28 Oct 2005 11:31:34 +0200
From: Andreas Korneliussen <Andreas.Korneliussen@Sun.COM>
Subject: Re: [jira] Commented: (DERBY-231) "FOR UPDATE" required for updatable
 result set to work
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> How this interacts with the statement cache needs to be considered. The
> current statement cache is lookup by current schema and text of the
> query string. You may be going in a direction where the same text
> 'SELECT * FROM T' leads to different plans depending on the updatable
> state of the result set.
>

I would need to check further into that, however I think that by making 
the new field for concurrency mode part of the identity of the 
GenericStatement, the cache would be correct.

> 
>>2. If the concurrency mode for the java.sql.Statement object is CONCUR_READ_ONLY, the updatemode will be set to READ_ONLY. If the query string contains "for update" an error will be thrown.
> 
> 
> That would be incorrect.
>   1) Derby still needs to support positioned UPDATE and DELETE, in that
> case it is fine to have a FOR UPDATE clause with a read only ResultSet.
>

You are right, it should not throw an error there.
I will modify the suggestion:

2. If the concurrency mode for the java.sql.Statement object is 
CONCUR_READ_ONLY, the updatemode will be set to READ_ONLY if the 
updateclause is unspecified or "for read only".  If the query string 
contains "for update" the updatemode is UPDATABLE, however the 
java.sql.ResultSet.updateXXX methods throws an exception (if called) 
since the resultset is not updatable.


>   2) Applications use the FOR UPDATE clause to control locking for
> future updates with read only ResultSets.
>

Note currently it throws an exception if the statement is not updatable 
i.e contains a join or order by.

-- Andreas

> 
> Dan.
>