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From "Kathey Marsden (JIRA)" <j...@apache.org>
Subject [jira] Updated: (DERBY-252) polishing up idea of default value including auto increment of a column in table
Date Thu, 07 May 2009 21:20:45 GMT

     [ https://issues.apache.org/jira/browse/DERBY-252?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Kathey Marsden updated DERBY-252:
---------------------------------

    Component/s:     (was: Documentation)
                 SQL

I think this is  a recommendation for an implementation change, not a user doc issue.  Changing
the component to SQL.


> polishing up idea of default value including auto increment of a column in table
> --------------------------------------------------------------------------------
>
>                 Key: DERBY-252
>                 URL: https://issues.apache.org/jira/browse/DERBY-252
>             Project: Derby
>          Issue Type: Task
>          Components: SQL
>            Reporter: Tomohito Nakayama
>            Priority: Minor
>
>  This is not bug. However, there exists some complexity in the part of default value
and autoincrement value in current implementation of derby.
>  Aside from whether any modification to be done or not for this issue, polishing up the
idea of default including autoincrement would be help thinking about default and autoincrement.
> Next is my idea for default...
>  "default value of the column" is value which registered to the column when a record
was inserted without any value.
>  "default value of the column" can be one of the next.
>   def_1: default does not exist
>   def_2: constant value
>   def_3: generated by a rule
>   def_3-1: autoincrement value
>   def_3-2: value generated by more complex rule than autoincrement (This does not exists
in derby)
>  There exists question wheter def_3 is truly default or not.
>  In the current implementation of derby, object interfaced as "org.apache.derby.catalog.DefaultInfo"
was externalized to "COLUMNDEFAULT" of "SYS_COLUMNS" in the case of def_2, and the object
have information of what constant value is used as default value.
>  On the other hand, information about autoincrement value was stored to "IDENTITYCOLUMNVALUE",
"IDENTITYCOLUMNSTART", "IDENTITYCOLUMNINC" of "SYS_COLUMNS".
>  There exists question in the case of def_3, why information about autoincrement value
does not exist in DefaultInfo.
>  One answer for this question is that storing information in "IDENTITYCOLUMNVALUE" to
DefaultInfo would cause performance trouble, because this will cause re-storing all information
of DefaultInfo always when record was inserted and next autoincrement value was prepared.

>  But this answer does not explan about information of "IDENTITYCOLUMNSTART", "IDENTITYCOLUMNINC".

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