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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Thu, 13 Nov 2008 23:44:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12647466#action_12647466
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Dag H. Wanvik commented on DERBY-481:
-------------------------------------

I read the specification again, clear and easy to read!

Some notes:

- Overview
  2nd sentence. Maybe add ALTER TABLE as well.
  3rd sentence. "The user declares" -> "The user can declare"

- SQL standard:
  Add sections 11.8, 11.39
  Reference to section 14.18 should be to 11.18, I think

- syntax:
  generation-clause ::= GENERATED ALWAYS ( value-expression )
  ************************************* "AS" keyword required after ALWAYS but missing

- SYSCOLUMNS:
  no new column was added, so I guess this section should be modified to
  reflect the implementation now?

- Documentation 

  If we decide REVOKE execute privilege from <role> will impact functions
  references in generated columns (as in dropping them), this should probably be documented
  along with the new doc for REVOKE <priv> from <role> and DROP
  <role>.

  Add note in INSERT on the use of "default", perhaps?
  
Appendix A: Possibly Non-deterministic System Functions
  - add CURRENT SCHEMA
  - add CURRENT SQLID


> implement SQL generated columns
> -------------------------------
>
>                 Key: DERBY-481
>                 URL: https://issues.apache.org/jira/browse/DERBY-481
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>    Affects Versions: 10.0.2.1
>            Reporter: Rick Hillegas
>            Assignee: Rick Hillegas
>         Attachments: derby-481-00-aa-prototype.diff, derby-481-01-aa-catalog.diff, derby-481-02-aa-utilities.diff,
derby-481-03-aa-grammar.diff, derby-481-04-aa-insert.diff, derby-481-05-aa-update.diff, derby-481-06-aa-genreferences.diff,
derby-481-07-aa-noSQLinRoutines.diff, derby-481-07-ab-noSQLinRoutines.diff, derby-481-08-aa-castToDeclaredType.diff,
derby-481-09-aa-dummyDefaults.diff, derby-481-10-aa-foreignKeyActions.diff, derby-481-11-aa-notNull.diff,
derby-481-12-aa-padding.diff, derby-481-13-aa-alterDatatype.diff, derby-481-14-ab-dropColumn.diff,
derby-481-15-aa-renameAndAddDefault.diff, derby-481-16-aa-dropFunction.diff, GeneratedColumns.html
>
>
> Satheesh has pointed out that generated columns, a SQL 2003 feature, would satisfy the
performance requirements of Expression Indexes (bug 455). Generated columns may not be as
elegant as Expression Indexes, but they are easier to implement. We would allow the following
new kind of column definition in CREATE TABLE and ALTER TABLE statements:
>     columnName GENERATED ALWAYS AS ( expression )
> If expression were an indexableExpression (as defined in bug 455), then we could create
indexes on it. There is no work for the optimizer to do here. The Language merely has to compute
the generated column at INSERT/UPDATE time.

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