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https://issues.apache.org/jira/browse/DERBY-5403?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Myrna van Lunteren updated DERBY-5403:
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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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