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From "Bernd Ruehlicke (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-118) Allow any build-in function as default values in table create for columns
Date Mon, 10 Jan 2005 19:18:12 GMT
Allow any build-in function as default values in table create for columns
-------------------------------------------------------------------------

         Key: DERBY-118
         URL: http://issues.apache.org/jira/browse/DERBY-118
     Project: Derby
        Type: Improvement
    Reporter: Bernd Ruehlicke
    Priority: Minor


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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