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https://issues.apache.org/jira/browse/DERBY-789?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12840561#action_12840561
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Knut Anders Hatlen commented on DERBY-789:
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I think the relevant section in SQL:2003 is 11.7 <unique constraint definition>.
It talks about both PRIMARY KEY and UNIQUE as uniqueness constraints. Further,
syntax rule 3b says:
> The set of columns in the <unique column list> shall be distinct from the
> unique columns of any other
> unique constraint descriptor that is included in the base table descriptor of
> T.
So it seems allowing PRIMARY KEY and UNIQUE on the same set of columns would be
a non-standard extension. It may still be useful, as it makes it easier to port
applications to Derby, but we cannot expect any advice from the standard as to
what's the correct behaviour for DROP CONSTRAINT on such constraints (I would
argue, though, that the MySQL/PrimaryImpliesUnique.diff behaviour is more
intuitive than the PostgreSQL behaviour.)
> Usability issue: "Constraints have the same set of columns"
> -------------------------------------------------------------
>
> Key: DERBY-789
> URL: https://issues.apache.org/jira/browse/DERBY-789
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Øystein Grøvlen
> Assignee: Bryan Pendleton
> Priority: Minor
> Attachments: PrimaryImpliesUnique.diff
>
>
> Legolas Woodland reported on derby-user that derby return errors like :
> org.apache.derby.client.am.SqlException: Constraints
> 'SQL060103004635123' and 'SQL060103004635121' have the same set of
> columns, which is not allowed.
> He got this when creating a table like this:
> create table WEBSITES (USERID integer not null unique, WEBSITEID
> bigint not null unique, DOMAINNAME varchar(255) not null unique,
> DESCRIPTION varchar(255), PPVIEW double, PPCLICK double, PPWEEK
> double, totalClick bigint, totalView bigint, active smallint, primary
> key (WEBSITEID));
> Omitting the unique specifier made things work.
> I think this is a usability issue. At least, one should not present names
> to the user, that has been generated internally. Instead, it would be
> helpful if the names of the columns involved was mentioned. I see two ways to
> solve this:
> 1. Return error that says that duplicate contraints on the following columns
> are not allowed.
> 2. Allow this and use same index for both constraints. (I guess dropping
> constraints will be more complicated in this case since one will have to
> check if other constraints are using the same index.)
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