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From "Knut Anders Hatlen (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-118) Allow any build-in function as default values in table create for columns
Date Wed, 30 May 2012 08:05:24 GMT

    [ https://issues.apache.org/jira/browse/DERBY-118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13285484#comment-13285484
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Knut Anders Hatlen commented on DERBY-118:
------------------------------------------

I don't see any obvious problems with making Derby's type conversion in DEFAULT clauses more
liberal. That is, except that it might trick users into writing non-portable SQL. I don't
feel strongly for or against any of the alternatives, so I'd be fine both with leaving it
as it is and with making the conversions more symmetric.

However, the patch only partially addresses the asymmetry, as far as I can see. It adds special
handling of conversions to string data types, but INSERT seems to accept other conversions
too, like float->int, which we currently don't allow in DEFAULT clauses. If we decide that
we want to allow implicit type conversion in DEFAULT clauses, we should probably do it for
all types.
                
> Allow any build-in function as default values in table create for columns
> -------------------------------------------------------------------------
>
>                 Key: DERBY-118
>                 URL: https://issues.apache.org/jira/browse/DERBY-118
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>            Reporter: Bernd Ruehlicke
>            Assignee: Dag H. Wanvik
>            Priority: Minor
>         Attachments: derby-118.diff, derby-118.stat, derby-118b.diff, derby-118b.stat,
derby-118c.diff, derby-118c.stat
>
>
> It is ok in ij to do a   values char(current_date)   but is is not allowed to use char(current_date)
as default value for clolumns; like for example
> CREATE TABLE DOSENOTWORK (num int, created_by varchar(40) default user, create_date_string
varchar(40) default char(current_date))
> Request: It should be allowed to use any build-in function which return a valid type
as part of the default value spec.
> There was a e-mail thread for this and the core content/answer was:
> Bernd Ruehlicke wrote:
> > 
> > CREATE TABLE DOSENOTWORK (num int, created_by varchar(40) default 
> > user, create_date_string varchar(40) default char(current_date))
> > 
> > give an error as below - any idea why ?!??!
> > 
> The rules for what is acceptable as a column default in Derby say that the only valid
functions are datetime functions. 
>   The logic that enforces this can be seen in the "defaultTypeIsValid" method of the
file:
> ./java/engine/org/apache/derby/impl/sql/compile/ColumnDefinitionNode.java
> The Derby Reference Manual also states this same restriction (albeit rather briefly):
> ----
> Column Default
> For the definition of a default value, a ConstantExpression is an expression that does
not refer to any table. It can include constants, date-time special registers, current schemas,
users, and null.
> ----
> A "date-time special register" here means a date-time function such as "date(current_date)"
in your first example. 
> Since the function "char" is NOT a date-time function, it will throw an error.
> I believe this restriction was put in place as part of the "DB2 compatibility" work was
that done in Cloudscape a while back.
> Hope that answers your question,
> Army

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