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https://issues.apache.org/jira/browse/DERBY-532?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13719335#comment-13719335
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Dag H. Wanvik edited comment on DERBY-532 at 7/25/13 7:39 AM:
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Uploading a functional specification for this, with some implementations ideas.
I'd like to try to build deferrable unique constraints in a first increment;
but the specification covers all supported types.
It seems it would desirable to avoid dropping a unique supporting index if few
rows are modified; options include temporarily making it non-unique (hard?) and
vice versa at commit, or using a temporary shadow table (would complicate
updates and selects).
was (Author: dagw):
Uploading a functional specification for this, with some implementations
ideas. I'd like to try to build deferrable unique constraints in a first
increment; but the specification covers all supported types.
It seems it would desirable to avoid dropping a unique supporting index if few
rows are modified; options include temporarily making it non-unique (hard?) and
vice versa at commit, or using a temporary shadow table (would complicated
updates and selects).
> Support deferrable constraints
> ------------------------------
>
> Key: DERBY-532
> URL: https://issues.apache.org/jira/browse/DERBY-532
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Jörg von Frantzius
> Labels: derby_triage10_11
> Attachments: deferredConstraints.html
>
>
> In many situations it is desirable to have constraints checking taking place
> only at transaction commit time, and not before. If e.g. there is a chain of
> foreign key constraints between tables, insert statements have to be ordered
> to avoid constraint violations. If foreign key references are circular, the
> DML has to be split into insert statements and subsequent update statements
> by the user.
> In other words, with deferred constraints checking, life is much easier for
> the user. Also it can create problems with softwares such as
> object-relational mapping tools that are not prepared for statement ordering
> and thus depend on deferred constraints checking.
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