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From "Myrna van Lunteren (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (DERBY-5403) implement further syntax for truncate table support - identityBehavior clause
Date Tue, 06 Sep 2011 17:03:17 GMT

     [ https://issues.apache.org/jira/browse/DERBY-5403?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Myrna van Lunteren updated DERBY-5403:
--------------------------------------

    Priority: Minor  (was: Major)

> implement further syntax for truncate table support - identityBehavior clause
> -----------------------------------------------------------------------------
>
>                 Key: DERBY-5403
>                 URL: https://issues.apache.org/jira/browse/DERBY-5403
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Myrna van Lunteren
>            Priority: Minor
>
> Since 10.7 basic support for TRUNCATE TABLE has been implemented (see DERBY-268) and
documented (see DERBY-4802).
> However, according to the SQL Standard (F200 in SQL:2008) the full syntax includes an
identityBehavior clause:
> TRUNCATE TABLE tableName [ identityBehavior ]
> identityBehavior ::=
>    CONTINUE IDENTITY
>    | RESTART IDENTITY 
> This clause has not been fully implemented.
> Reading through DERBY-268 yields more details, e.g.:
> (https://issues.apache.org/jira/browse/DERBY-268?focusedCommentId=12905937&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12905937):
> "A follow-on effort might be to implement the optional CONTINUE IDENTITY and RESTART
IDENTITY clauses. Fortunately, the tricky bit of RESTART IDENTITY has already been implemented.
The tricky bit is the following implied statement which is executed after truncating the table:
> ALTER TABLE tableName ALTER COLUMN RESTART WITH initialValue "
> and:
> (https://issues.apache.org/jira/browse/DERBY-268?focusedCommentId=12912378&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12912378)
"[...]sqlgrammar.jj would be a good starting point"
> and:
> ( https://issues.apache.org/jira/browse/DERBY-268?focusedCommentId=12916134&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-12916134):
> [...]all of this code should be in the engine. The good news is that both TRUNCATE TABLE
and ALTER TABLE ALTER COLUMN RESTART are handled by the AlterTableConstantAction machinery
at run time. If I were tackling this, I would first try something along these lines:
> o AlterTableNode.bindStatement() will need to build a tableElementList structure for
TRUNCATE TABLE, describing the identity column which needs to be re-initialized. For ALTER
TABLE ALTER COLUMN RESTART, that tableElementList is created by the parser.
> o That tableElementList structure will then be picked up by AlterTableNode.prepConstantAction
and turned into a ColumnInfo array when the run time structures are generated for TRUNCATE
TABLE. The ColumnInfo[] structure should contain enough information to describe the change
to the identity column.
> o The column info structure will then be processed by AlterTableConstantAction.executeConstantAction()
at run time.
> You may need to tweak the code a bit to get this to function, but I think this basic
processing flow should work.[...]"
> and the comments in DERBY-268 after Oct 10, 2010 all refer to an aborted attempt by Eranda
to work on this functionality, including a tentative patch.
> I'll mark this issue beginner because of that preliminary work.

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