[jira] [Commented] (DERBY-118) Lift some DB2 restrictions on DEFAULT values [was: Allow any build-in function as default values in table create for columns]

["Knut Anders Hatlen (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-118?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13287414#comment-13287414 ] 

Knut Anders Hatlen commented on DERBY-118:
------------------------------------------

Does insert too have special handling of each conversion, or does it wrap the value in a cast node (or use some equivalent mechanism) when the types don't match exactly? If we could just wrap the default value in a cast node and be done with it, it might simplify the code and also be easier to keep consistent with insert. That would also make CREATE TABLE detect if a character literal is too long to fit in the column, I think. But I haven't checked if a cast would match exactly the conversion done by insert.
                
> Lift some DB2 restrictions on DEFAULT values [was: 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-all-defaults.diff, 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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