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From "Christian d'Heureuse (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4) "order by" is not supported for "insert ... select"
Date Sat, 19 May 2007 16:31:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12497168
] 

Christian d'Heureuse commented on DERBY-4:
------------------------------------------

> But it will restrain us from some optimizations in the future, 

I don't agree. An INSERT ... SELECT without an "ORDER BY" can still be optimized with parallel
processing in the future. Only the new "INSERT ... SELECT ... ORDER BY" cannot be processed
in parallel.

> insert into temp2 select count(b.s), a.s from temp1 a, temp1 b where b.s <= a.s group
by a.s

This would be an alternative, but it's very slow for large tables, because the complexity
is in the order of O(n*(n/2)).

> "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
>
>
> 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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