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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-481) implement SQL generated columns
Date Tue, 28 Oct 2008 14:04:46 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-481-05-aa-update.diff

Attaching derby-481-05-aa-update.diff, the last chunk from the prototype patch. I am running
regression tests now.

This patch wires in UPDATE support for generated columns. As with INSERT, I threaded my way
through the UPDATE machinery largely by following the way that CHECK constraints are handled.

UPDATE presents a couple extra issues in addition to the issues raised by INSERT:

1) We don't have to enhance the target row with defaulted columns. Instead, we have to enhance
the update list with all generated columns whose generation clauses reference columns in the
update list.

2) If a generated column is added to the update list, then the columns it references must
be added to the list of columns which are read from the base row.

3) The target row for UPDATE holds two copies of each column that either has to be written
or read: the before value of the column and the after value. This gives rise to some trickiness.

Touches the following files:


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

Adds generated columns to the update list if they are affected by the update. For all generated
columns in the update list, adds the columns they reference to the list of columns to be read
from disk. Forbids the setting of a generated column to anything except the DEFAULT literal.
Generates a method to fill in computed columns at execution time--this is the (2') method
described above in the summary of patch derby-04-aa-insert.diff.


M      java/engine/org/apache/derby/iapi/sql/execute/ResultSetFactory.java
M      java/engine/org/apache/derby/impl/sql/execute/GenericResultSetFactory.java

Adds the (2') method as an argument to the factory methods that create UpdateResultSets.

M      java/engine/org/apache/derby/impl/sql/execute/UpdateResultSet.java

Invokes (2') close to where we invoke (3') already.


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

Uncommented basic tests for updates. Uncommented basic tests for the interaction of generated
columns with triggers and foreign keys.

> 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, 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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