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From "Dag H. Wanvik (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-118) Allow any build-in function as default values in table create for columns
Date Thu, 31 May 2012 21:14:23 GMT

    [ https://issues.apache.org/jira/browse/DERBY-118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13286950#comment-13286950
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Dag H. Wanvik commented on DERBY-118:
-------------------------------------

Thanks, Knut. I already added an test case for CHAR, also adopted your suggestion of Formatters.repeatChar().

Uploading a patch derby-118-all-defaults, which removes the all (I believe) DB2 restrictions
in the DEFAULT clause, iff the restriction does not apply at insert time.  This makes Derby
more liberal, as discussed, but symmetric.

(*) Another thing is that more checks could be made as table creation time (rather than at
insert time), since we are mostly talking literals here, and even the datetime functions have
predictable (modulo locale?)  lengths. This is an existing weakness, and I do not to intend
to address that improvement in this JIRA.

List of restrictions lifted:

- datetime builtins can be used for CHAR and VARCHAR columns

- loss of precision in default value when used for a decimal column

- allow float literals to be used as default for INT, BIGINT columns.  Interestingly, this
was not restricted for SMALLINT, maybe unintentionally.

- allow string literals longer than 254 for VARCHAR columns.  Truncation checks will still
happen at insert time. Note that this makes the (valid) check for strings longer than 254
for CHAR columns move to INSERT time. I could reintroduce this at create time, since it changes
the behavior in a "negative" way. Note that most truncation checks already happened at insert
time; this particular check, even is performed, is no guarantee, unless the CHAR type is CHAR(254).
 A string of say, 200, would still be caught at insert time if the type is CHAR(199), so the
move makes the checking more regular, if sometimes delayed, but cf. item (*) above.

Added positive and negative tests for the above.

Running regressions.


                
> 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-longvarchar.diff, 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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