implement further syntax for truncate table support - identityBehavior clause
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Key: DERBY-5403
URL: https://issues.apache.org/jira/browse/DERBY-5403
Project: Derby
Issue Type: Improvement
Components: SQL
Reporter: Myrna van Lunteren
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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