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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-481) implement SQL generated columns
Date Wed, 12 Nov 2008 17:49:44 GMT

    [ https://issues.apache.org/jira/browse/DERBY-481?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12646973#action_12646973
] 

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

I agree.

Another thing:

What is the correct behavior for this case? Here the generation
expression needs a privilege which gets revoked...

ij(CONNECTION0)> create table t (i int, j int, k int generated always as (dag.myfunc(j)));
ERROR 42504: User 'KNUT' does not have execute permission on FUNCTION 'DAG'.'MYFUNC'.
ij(CONNECTION0)> set role bar; -- this role has the privilege and is granted to KNUT earlier
0 rows inserted/updated/deleted
ij(CONNECTION0)> create table t (i int, j int, k int generated always as (dag.myfunc(j)));
0 rows inserted/updated/deleted
ij(CONNECTION0)> set connection connection1;
ij(CONNECTION1)> revoke bar from knut;
0 rows inserted/updated/deleted
ij(CONNECTION1)> set connection connection0;
ij(CONNECTION0)> insert into t values (1,2,default);
ERROR 42504: User 'KNUT' does not have execute permission on FUNCTION 'DAG'.'MYFUNC'.

Triggers, view and constraints in similar circumstances get dropped; should the generated
column get dropped too?


> 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, 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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