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