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From "Mamta A. Satoor (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-4988) ALTER TABLE DROP COLUMN should make use of information in SYSTRIGGERS to detect column used through REFERENCING clause to find trigger dependencies
Date Wed, 02 Feb 2011 05:41:29 GMT

    [ https://issues.apache.org/jira/browse/DERBY-4988?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12989522#comment-12989522
] 

Mamta A. Satoor commented on DERBY-4988:
----------------------------------------

I will look at backporting this jira to 10.7 once the tests have run successfully on IBM and
Sun machines for few nights. They ran fine on my windows XP machine with IBM 16 jdk.

Also, the changes for this jira should not be backported further back than 10.7. Prior to
10.7, we didn't keep track of trigger action column used through REFERENCING clause and the
changes for this jira relies on that information,

> ALTER TABLE DROP COLUMN should make use of information in SYSTRIGGERS to detect column
used through REFERENCING clause to find trigger dependencies
> ---------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-4988
>                 URL: https://issues.apache.org/jira/browse/DERBY-4988
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.7.1.1
>            Reporter: Mamta A. Satoor
>            Assignee: Mamta A. Satoor
>             Fix For: 10.8.0.0
>
>
> At the time of ALTER TABLE DROP COLUMN, Derby checks if the column being dropped in a
trigger column and if so, then it will not drop the column if it is being done in RESTRICT
mode or it will drop the trigger while dropping the column in CASCADE mode. This does not
implement SQL standard to it's entirety. 
> **************************************
> SQL standard says following about ALTER TABLE DROP COLUMN RESTRICT and trigger dependency
in CREATE TRIGGER section 
> If RESTRICT is specified, then C shall not be referenced in any of the following 
> d) Either an explicit trigger column list or a triggered action column set of any trigger
descriptor. 
> (The triggered action column set included in the trigger descriptor is the set of all
distinct, fully qualified names of columns contained in the <triggered action>.) 
> **************************************
> What is missing from Derby implementation from SQL standard point of view is detected
triggered action column set.
> Starting 10.7(with DERBY-1482), Derby started keeping track of trigger action columns
which are referenced through REFERENCING clause. This information can be used to improve the
behavior of ALTER TABLE DROP COLUMN in 10.7 and higher. This will not cover all the trigger
action columns since columns referenced without the REFERENCING clause are not tracked anywhere
at this point. More work will need to be done to implement SQL standard completely. But we
can take a step forward by using the information available in 10.7 and higher to detect trigger
action columns which are referenced through REFERENCING clause

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