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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Sat, 15 Nov 2008 01:04:48 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12647780#action_12647780

Dag H. Wanvik commented on DERBY-481:

Reviewed derby-481-03-aa-grammar.diff, looks good! Interesting to see more of the compile-time
mechinery involved here.

Minor notes:

* DDLStatementNode.java
makeFromList javadoc misses @param for 2 parameters

* TableElementList.java
- This comment in bindAndValidateGenerationClauses is a cut/paste palimpsest:
  // bind the check condition
  // verify that it evaluates to a boolean

- Shouldn't finally clause in bindAndValidateGenerationClauses also
  reset the current auxiliary provider list?

* StaticMethodCallNode.java
- two spurious blank line diffs

* GenerationClauseNode.java
toString should include "AS" keyword after ALWAYS.

* GeneratedColumnsTest.java
- It would be nice to add a comment that the test can not be run
  in client server mode due to the casting to internal Derby objects
  of some result set columns for dictionary tables.

* DB_Table.java

Will an unqualified function name necessarily be output correctly by
dblook? Do we need to expand the generation text in SYSCOLUMN to
include the fully qualified name for functions?

> 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:
>            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,
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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