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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Wed, 12 Nov 2008 15:31:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646929#action_12646929
] 

Rick Hillegas commented on DERBY-481:
-------------------------------------

Thanks for finding this issue with BEFORE triggers, Dag. I don't understand why the standard
forbids these references in BEFORE triggers. This would be a good question to ask the SQL
committee. I think we should follow the standard here. We can relax this restriction later
if we come to understand that it really is harmless.

> 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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