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https://issues.apache.org/jira/browse/DERBY-6371?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13915169#comment-13915169
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Myrna van Lunteren commented on DERBY-6371:
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I am looking at backporting this one.

> DROP COLUMN looks in wrong schema when checking trigger dependencies
> --------------------------------------------------------------------
>
>                 Key: DERBY-6371
>                 URL: https://issues.apache.org/jira/browse/DERBY-6371
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.10.1.1
>            Reporter: Knut Anders Hatlen
>            Assignee: Knut Anders Hatlen
>             Fix For: 10.11.0.0
>
>         Attachments: compSchema.diff, derby-6371-1a.diff, derby-6371-2a.diff
>
>
> If you define a trigger in another schema than the current schema, and the 
> trigger action references tables in the current schema without explicit 
> schema names, ALTER TABLE DROP COLUMN may get confused when checking 
> dependencies.
> For example:
> ij> create table s1.t1(x int, y int);
> 0 rows inserted/updated/deleted
> ij> create table s1.t2(x int, y int);
> 0 rows inserted/updated/deleted
> ij> set schema s1;
> 0 rows inserted/updated/deleted
> ij> create trigger s2.tr after update of x on t1 for each row insert into 
> t2(x) select x from t1;
> 0 rows inserted/updated/deleted
> ij> alter table s1.t1 drop column y restrict;
> ERROR X0Y25: Operation 'DROP COLUMN' cannot be performed on object 'Y' 
> because TRIGGER 'TR' is dependent on that object.
> The ALTER TABLE statement should have succeeded, because the trigger does not 
> depend on column Y.
> If you create dummy tables in S2 with the same names as those in S1, the same 
> ALTER TABLE statement succeeds:
> ij> create table s2.t1(x int);
> 0 rows inserted/updated/deleted
> ij> create table s2.t2(x int);
> 0 rows inserted/updated/deleted
> ij> alter table s1.t1 drop column y restrict;
> 0 rows inserted/updated/deleted
> The existence of these unrelated tables should not affect whether you're 
> allowed to drop the column.



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