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https://issues.apache.org/jira/browse/DERBY-6559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13991059#comment-13991059
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Dag H. Wanvik edited comment on DERBY-6559 at 5/6/14 8:06 PM:
--------------------------------------------------------------
Thanks, Knut. Yes, I was wondering about whether there was some implicit commit
there, but I didn't get to looking it up. Good to get that clarified.
I also tried Postgresql on this with this result:
{code}
> create table t(i int, j int, constraint c primary key(i) deferrable);
> create table child(i int, constraint fk foreign key(i) references t(i) on
> delete set null);
ERROR: cannot use a deferrable unique constraint for referenced table "t"
{code}
So, they avoid the issue by being restrictive.
Documented in http://www.postgresql.org/docs/9.3/static/sql-createtable.html:
{quote}
The referenced columns must be the columns of a non-deferrable unique or
primary key constraint in the referenced table.
{quote}
was (Author: dagw):
Thanks, Knut. Yes, I was wondering about whether there was some implicit commit
there, bu tI didn't get to looking it up. Good to get that clarified.
I also tried Postgresql on this with this result:
{code}
> create table t(i int, j int, constraint c primary key(i) deferrable);
> create table child(i int, constraint fk foreign key(i) references t(i) on
> delete set null);
ERROR: cannot use a deferrable unique constraint for referenced table "t"
{code}
So, they avoid the issue by being restrictive.
Documented in http://www.postgresql.org/docs/9.3/static/sql-createtable.html:
{quote}
The referenced columns must be the columns of a non-deferrable unique or
primary key constraint in the referenced table.
{quote}
> A immediate Fk constraint blows up iff its referenced PK is deferred and we
> delete a duplicate
> ----------------------------------------------------------------------------------------------
>
> Key: DERBY-6559
> URL: https://issues.apache.org/jira/browse/DERBY-6559
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Reporter: Dag H. Wanvik
> Assignee: Dag H. Wanvik
>
> Cf the following test case:
> {code:title=testFKPlusUnique|borderStyle=solid}
> /**
> * The referenced constraint (in the referenced table) is also a deferred
> * (unique/ok) constraint.
> *
> * @throws SQLException
> */
> public void testFKPlusUnique() throws SQLException {
> Statement s = createStatement(
> ResultSet.TYPE_FORWARD_ONLY, ResultSet.CONCUR_UPDATABLE);
>
> try {
> s.executeUpdate(
> "create table ref_t(i int, " +
> " constraint ct primary key(i) deferrable initially
> deferred)");
> s.executeUpdate(
> "create table t(i int unique not null, " +
> " constraint c foreign key (i) references ref_t(i) " +
> " deferrable initially immediate)");
>
> s.executeUpdate("insert into ref_t values 1,1");
> s.executeUpdate("insert into t values 1");
>
> // Now, the child (referencing table) is referencing one of the
> the
> // rows whose value is 1, so the reference is potentially suspect.
>
> // What happens when we delete the one copy before commit?
> ResultSet rs = s.executeQuery("select * from ref_t");
> rs.next();
>
> // Will this delete blow up? Hopefully not, here is another row
> // that would satisfy the constraint.
> rs.deleteRow();
>
> // Now there should be only one left, so the referenced table is
> // OK.
> commit();
> :
> {code}
> Now, the constraint C throws when we do the "rs.deleteRow" above. But since
> there is (still) a row satisfying the FK, albeit a duplicate, I believe it
> should not.
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