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