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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4) "order by" is not supported for "insert ... select"
Date Tue, 22 May 2007 01:03:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12497655
] 

Bryan Pendleton commented on DERBY-4:
-------------------------------------

Mike asked: "The current implementation happens to return increasing keys, but do we ever
guarantee that, and should we?"

I believe the answer is that we guarantee to obey the START WITH and 
INCREMENT BY attributes of the generated column At:
http://db.apache.org/derby/docs/dev/ref/rrefsqlj37836.html#rrefsqlj37836
we say "For SMALLINT, INT, and BIGINT columns with identity attributes, Derby automatically
assigns increasing integer values to the column."

Later, we also say: "And if you specify a negative number for the increment value, Derby decrements
the value with each insert. If this value is positive, Derby increments the value with each
insert. "

It's hard to see how to interpret the "START WITH" and "INCREMENT BY"
attributes of the generated column spec without providing such guarantees. 
INCREMENT BY 1 needs to increment by 1.

I agree with you that relaxing these guarantees could allow higher-performing
implementations in the future.

But I think that many applications are already depending on the current behavior of the
START WITH and INCREMENT BY properties.

> "order by" is not supported for "insert ... select"
> ---------------------------------------------------
>
>                 Key: DERBY-4
>                 URL: https://issues.apache.org/jira/browse/DERBY-4
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>            Reporter: Christian d'Heureuse
>         Assigned To: Bryan Pendleton
>            Priority: Minor
>         Attachments: insertOrderBy.diff, insertOrderBy_v2.diff, samples.ij
>
>
> When filling a table with "insert ... select ...", "order by" cannot be specified.
> There is not method to copy a table sorted into another table (except using export/import).
This would be useful to optimize performance for big tables, or to create identity values
that are ascending (related to another column).
> Example:
> create table temp1 (
>    s varchar(10));
> insert into temp1 values 'x','a','c','b','a';
> create table temp2 (
>    i integer not null
>       generated always as identity
>       primary key,
>    s varchar(10));
> insert into temp2 (s)
>    select s from temp1 order by s;
> --> Error: "order by" is not allowed.
> -- trying to use "group by" instead of "oder by":
> insert into temp2 (s)
>    select s from temp1 group by s;
> select * from temp2;
> --> "group by" did not sort the table.

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