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From "ASF subversion and git services (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6742) For update statement, collect generated keys if Statement.RETURN_GENERATED_KEYS flag is supplied to the JDBC call.
Date Thu, 18 Sep 2014 03:53:34 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6742?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14138455#comment-14138455

ASF subversion and git services commented on DERBY-6742:

Commit 1625884 from [~mamtas] in branch 'code/trunk'
[ https://svn.apache.org/r1625884 ]

CERBY-6414(Incorrect handling when using an UPDATE to SET an identity column to DEFAULT)

I have created DERBY-6742 for JDBC part of this feature so we can generate auto generated
resultset for an update statement updating generated columns. This implementation is supported
through Statement.RETURN_GENERATED_KEYS flag.

Junit tests for this feature are in GeneratedColumnsTest.java. Upgrade tests are in Changes10_12.java.
Upgrade test shows that a soft upgrade from pre-10.11 will not support update of generated
columns using DEFAULT but 10.11 to trunk soft upgrade will allow it. This is because starting
10.11, we have started using sequence generator to create unique ids. If we want to support
updating of idetity columns for pre-10.11 releases, we will need to maintain the code for
old way of generating unique ids. In order to avoid that, this feature is available to only
10.11 db during soft upgrade.

For UPDATE of identity column to work in the MERGE sql, we need to make changes to MERGE code(DERBY-6743).
MERGE already has required code for insert putting DEFAULT in generated columns. Implementation
needs to be added for update putting DEFAULT in generated columns in case of MERGE. In the
mean time, I have renamed existing junit test test_015_bug_6414 to atest_015_bug_6414 in MergeStatementTest.java
so we do not run into failures.

Some detail about the part of the implementation that was tricky for DERBY-6414.
The existing code was originally written to handle inserting values in identity columns using
DEFAULT. In case of insert, InsertResultSet uses ColumnDescriptors in resultDescription to
find the type of the generated columns. This data structure holds the column descriptors of
all the columns in the table. All the columns are in this data structure because even though
INSERT statement may not explicitly assign a value to each and every column in the table,
all the columns end up getting some value in them through an INSERT statement. The code in
InsertResultSet.initializeAIcache method relies on availability of all the columns type information.
But in case of Update, resultDescription does not include all the columns in the table. It
only has the columns being touched by the Update statement(the rest of the columns in the
table will retain their original values), and for each of those touched columns, it has a
duplicate entry in resultDescription in order to have before and after values for the changed
column values. This difference in array content of resultDescription requires us to have separate
implementation of initializeAIcache method for insert and update.

> For update statement, collect generated keys if Statement.RETURN_GENERATED_KEYS flag
is supplied to the JDBC call.
> ------------------------------------------------------------------------------------------------------------------
>                 Key: DERBY-6742
>                 URL: https://issues.apache.org/jira/browse/DERBY-6742
>             Project: Derby
>          Issue Type: Improvement
>          Components: JDBC
>    Affects Versions:
>            Reporter: Mamta A. Satoor
>            Assignee: Mamta A. Satoor
> DERBY-6414 is providing SQL support to update identity columns using DEFAULT keyword.
This jira will look into collecting generated keys if Statement.RETURN_GENERATED_KEYS flag
is supplied to the JDBC call for an UPDATE sql.

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