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From "Erik Bengtson (JIRA)" <j...@apache.org>
Subject [jira] Commented: (JDO-246) JPOX eliminates duplicates in the query result although DISTINCT is not specified.
Date Wed, 01 Feb 2006 15:54:05 GMT
    [ http://issues.apache.org/jira/browse/JDO-246?page=comments#action_12364818 ] 

Erik Bengtson commented on JDO-246:
-----------------------------------

> I'm a little confused about the term intersection. Just for my understanding: do you
mean Cartesian product?

We are using intersection between Department.employees vs Employee, since we only retain
the employees that are on both sets.

Employee = {"Employee1","Employee2","Employee3"}
Department = {"dept1","dept2","dept3"}
Department.employees = {{"Employee1","Employee3"},{"Employee2"},{"Employee1","Employee2"}}


{"Employee1", "emp2Last"}
{"Employee3", null}
{"Employee2", "emp2Last"}
{"Employee1", "emp2Last"}
{"Employee2", "emp2Last"} 

A cartesian product would result in return all employees from Employee set for each Department.

> Here is my understanding of the semantics of your query including the resource variable.
Please note, this does not necessarily mean it needs to be implemented that way :-):

You are the JDOQL expert here ;). 

Now the second example, The way I exemplified I was thinking in a kind of outer join from
Employee vs Resource. Meaning returning a row if one of both has an element in the set.


{"Employee1", "emp2Last", "Resource2"}
{"Employee3", null, null}
{"Employee2", "emp2Last","Resource2"}
{null,null,"Resource3"}
{null,null,"Resource1"}
{"Employee1", "emp2Last","Resource1"}
{"Employee2", "emp2Last","Resource2"}


The way you did it is different, you take Employee vs Resource and calculates the Cartesian
product.

Then the query result would be:
{"Employee1", "emp2Last", "Resource2"}
{"Employee3", null, "Resource2"}
{"Employee2", "emp2Last","Resource2"}
{"Employee2", "emp2Last","Resource3"}
{"Employee2", "emp2Last","Resource1"}
{"Employee1", "emp2Last","Resource1"}
{"Employee1", "emp2Last","Resource2"}
{"Employee2", "emp2Last","Resource1"}
{"Employee2", "emp2Last","Resource2"}


>About the difference between uisng && or ||:
>I think with && only those tripels are retained where both the employee and the
resource have a relationship to the department of the triple. Using || the set of retained
tripels before the projection is bigger, because it also includes tripels where only one of
the two (employee, resource) is related to the department.

You mean an inner join if &&, and outer join ||

> Does this make sense?

I don't know. :(

We have these steps to calculate

1. Set e =Department.employees (Intersect) Employee
2. Set r =Departments.resources (Intersect) Resource
3. Set result = d (Cartesian Product) (e (Cartesian Product) r) (your example)

or

3. Set result = d (Cartesian Product) (e (outer join) r) (my example)

> JPOX eliminates duplicates in the query result although DISTINCT is not specified.
> ----------------------------------------------------------------------------------
>
>          Key: JDO-246
>          URL: http://issues.apache.org/jira/browse/JDO-246
>      Project: JDO
>         Type: Bug
>   Components: tck20
>     Reporter: Michael Watzek
>     Assignee: Erik Bengtson

>
> Test case NPEInResultExpr fails because the result of the query below is expected to
contain duplicates. JPOX eliminates the duplicates.
> 14:22:55,046 (main) DEBUG [org.apache.jdo.tck] - Executing API query: SELECT employee.manager.lastname
FROM org.apache.jdo.tck.pc.company.Department WHERE employees.contains(employee) VARIABLES
Employee employee 
> 14:22:55,078 (main) DEBUG [org.apache.jdo.tck] - Query result: [emp2Last, null]
> 14:22:55,078 (main) DEBUG [org.apache.jdo.tck] - Wrong query result: 
> expected: [emp2Last, null, emp2Last, emp2Last, emp2Last]
> got:      [emp2Last, null]
> 14:22:55,078 (main) INFO  [org.apache.jdo.tck] - Exception during setUp or runtest: 
> junit.framework.AssertionFailedError: Assertion A14.6.9-4 (NPEInResultExpr) failed: 
> Wrong query result: 
> expected: [emp2Last, null, emp2Last, emp2Last, emp2Last]
> got:      [emp2Last, null]
> 	at junit.framework.Assert.fail(Assert.java:47)
> 	at org.apache.jdo.tck.JDO_Test.fail(JDO_Test.java:546)
> 	at org.apache.jdo.tck.query.QueryTest.queryFailed(QueryTest.java:500)
> 	at org.apache.jdo.tck.query.QueryTest.checkQueryResultWithoutOrder(QueryTest.java:485)
> 	at org.apache.jdo.tck.query.QueryTest.execute(QueryTest.java:1189)
> 	at org.apache.jdo.tck.query.QueryTest.execute(QueryTest.java:1029)
> 	at org.apache.jdo.tck.query.QueryTest.executeAPIQuery(QueryTest.java:966)
> 	at org.apache.jdo.tck.query.QueryTest.executeAPIQuery(QueryTest.java:946)
> 	at org.apache.jdo.tck.query.result.NPEInResultExpr.testPositive(NPEInResultExpr.java:106)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
> 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
> 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
> 	at java.lang.reflect.Method.invoke(Method.java:324)
> 	at junit.framework.TestCase.runTest(TestCase.java:154)
> 	at org.apache.jdo.tck.JDO_Test.runBare(JDO_Test.java:204)
> 	at junit.framework.TestResult$1.protect(TestResult.java:106)
> 	at junit.framework.TestResult.runProtected(TestResult.java:124)
> 	at junit.framework.TestResult.run(TestResult.java:109)
> 	at junit.framework.TestCase.run(TestCase.java:118)
> 	at junit.framework.TestSuite.runTest(TestSuite.java:208)
> 	at junit.framework.TestSuite.run(TestSuite.java:203)
> 	at junit.framework.TestSuite.runTest(TestSuite.java:208)
> 	at junit.framework.TestSuite.run(TestSuite.java:203)
> 	at junit.textui.TestRunner.doRun(TestRunner.java:116)
> 	at junit.textui.TestRunner.doRun(TestRunner.java:109)
> 	at org.apache.jdo.tck.util.BatchTestRunner.start(BatchTestRunner.java:120)
> 	at org.apache.jdo.tck.util.BatchTestRunner.main(BatchTestRunner.java:95)

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