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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-481) implement SQL generated columns
Date Fri, 31 Oct 2008 22:01:47 GMT

     [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Rick Hillegas updated DERBY-481:
--------------------------------

    Attachment: derby-481-09-aa-dummyDefaults.diff

Attaching derby-481-09-aa-dummyDefaults.diff. This patch addresses a bug found by Dag: If
you tried to poke the literal DEFAULT into a generated column using an INSERT without a target
list (meaning all values in the row had to be specified), then we bombed trying to bind the
generation clause prematurely.


Touches the following files:

M      java/engine/org/apache/derby/impl/sql/compile/ResultColumnList.java

At the point where we substitute default values for DEFAULT literals, we just substitute an
untyped NULL for generation clauses. Later on, when we have enough context to bind the generation
clauses, we replace these NULLs with the actual generation clauses.


M      java/testing/org/apache/derbyTesting/functionTests/tests/lang/GeneratedColumnsTest.java

Tests for the problem case which Dag found.


> 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, 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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