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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Wed, 26 Nov 2008 16:58:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12651059#action_12651059
] 

Dag H. Wanvik commented on DERBY-481:
-------------------------------------

Reviewing derby-481-11-aa-notNull. Thanks for the good explanations,
Rick, really helped! Good patch.

Notes:

Index: java/engine/org/apache/derby/impl/sql/execute/NormalizeResultSet.java

Good that you refactored this class a bit; was a bit messy before..

* Javadoc for normalizeColumn starts with the text "Normalize a
  row". It should probably be "Normalize a column". What about the
  rest of that comment? It speaks of not yet having data type
  conversions.. Is this still relevant? We do have casts, but maybe
  this is something else. Asking since you touched it by moving it
  around ;-) 

* I think the normalizeColumn method should take sourceCol as an
  argument, rather than sourceRow (less scope; only one column is ever
  used inside normalizeColumn).

* normalizeColumn javadoc lacks @params and @return.
* private member numColumns is no longer needed.
* computeStartColumn lacks @return and @params.

Index: java/engine/org/apache/derby/impl/sql/execute/NoRowsResultSetImpl.java

* would be nice to comment usage of new members firstColumn,
  generatedColumnPositions, normalizedGeneratedValues

* maybe I am missing something here, but couldn't the two conditional
  actions below be put inside one 'if' in that they always happen together?

                if ( firstColumn < 0 ) { firstColumn = NormalizeResultSet.computeStartColumn(
isUpdate, activation.getResultDescription() ); }
                if ( generatedColumnPositions == null ) { setupGeneratedColumns( activation,
(ValueRow) newRow ); }

* Javadoc for setupGeneratedColumns could use some more explanation, a
  bit on the concise side now, I think. It has side-effects.


* The javadoc for ResultColumn#hasGenerationClause can now refer to
  the javadoc in the interface ResultColumnDescriptor (to avoid
  redundancy in description).


> 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, derby-481-17-aa-currentSchema.diff,
derby-481-18-aa-updatableResultSets.diff, derby-481-19-aa-cleanup.diff, GeneratedColumns.html,
GeneratedColumns.html, 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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