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https://issues.apache.org/jira/browse/DERBY-6340?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13788025#comment-13788025
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Dyre Tjeldvoll commented on DERBY-6340:
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Hi Rick, thank you for your comments.
I agree that the std does not mention comparison of distinct types to their
STs, so that a cast is required in this case. I have updated the fs
accordingly. I have also added a description of the the default identifiers for
the casting functions.
When it comes to the namespace of distinct UDT, I wondered if you could clear
up a few things:
My understanding of Part 2, section 11.51 (user-defined type definition),
general rule 2.b, is that the casting functions are created in the explicit or
implied schema of the UDT. "CREATE FUNCTION SN.FNUDT ( ... where: SN is the
explicit or implicit <schema name> of UDTN". Is DERBY-5901 the reason why the
name must not conflict with a builtin function or aggregate?
A couple of observations:
* Without the ability to specify <cast to source> you can create at most one
alias for each builtin type in the same schema?
* Due to DERBY-5901, we must either always specify <cast to source> or let the
default identifier be non-standard as the default names mandated by the
standard are already used by existing builtin functions in Derby?
Do you agree?
> Add support for CREATE TYPE AS <existing type> (synonym types)
> --------------------------------------------------------------
>
> Key: DERBY-6340
> URL: https://issues.apache.org/jira/browse/DERBY-6340
> Project: Derby
> Issue Type: Improvement
> Components: SQL
> Reporter: Dyre Tjeldvoll
> Assignee: Dyre Tjeldvoll
> Attachments: CreateTypeAs_fs_draft_2.html, CreateTypeAs_fs_draft.html
>
>
> The SQL standard (2003) chapter 11.41 <user-defined type definition> allows
> the creation of synonyms or aliases for an existing type: CREATE TYPE AS
> <predefined type>. By allowing this in Derby we would simplify migration
> from, and interoperation with, other databases.
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