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https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Rick Hillegas updated DERBY-481:
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Attachment: derby-481-01-aa-catalog.diff
Attaching derby-481-01-aa-catalog.diff, the first small patch cut out of the
prototype. Presented for review. Tests pass cleanly for me. Tests for these
catalog changes will appear in later patches.
This patch provides the catalog support for generated columns. Catalog support
turned out to be simpler than the functional spec imagined. There is no need to
add another column to SYS.SYSCOLUMNS. Instead, we can re-use the existing
COLUMNDEFAULT column to store the generation clause.
Touches the following files:
M java/engine/org/apache/derby/catalog/DefaultInfo.java
M java/engine/org/apache/derby/catalog/types/DefaultInfoImpl.java
Special constructor for default descriptors which describe generated columns. A
default descriptor can tell you whether it represents a generated column. If it
does, it can also tell you what other columns the generation clause references.
M java/engine/org/apache/derby/iapi/sql/dictionary/ColumnDescriptor.java
Column descriptors can now tell you if they are bound to generation clauses.
M java/engine/org/apache/derby/iapi/sql/dictionary/TableDescriptor.java
The table descriptor can now return a list of all the columns which have
generation clauses.
> 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, 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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