Question about org.apache.openjpa.jdbc.sql.DBDictionary.toNativeJoin(Join join) method

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Hi everybody,
I was trying to retrieve an object along with one of its many-to-one  
relation eagerly from the datastore.
Using a "database" JoinSyntax I always got the following exception:
org.apache.openjpa.persistence.PersistenceException: null
23:46:40,808 ERROR [STDERR] 	at  
org 
.apache.openjpa.jdbc.sql.DBDictionary.toNativeJoin(DBDictionary.java: 
2172)
23:46:40,808 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.SelectImpl.append(SelectImpl.java:1702)
23:46:40,808 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.DBDictionary.getWhere(DBDictionary.java: 
2061)
23:46:40,809 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.DBDictionary.toSelect(DBDictionary.java: 
2000)
23:46:40,809 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.SelectImpl.toSelect(SelectImpl.java:213)
23:46:40,809 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.SelectImpl.execute(SelectImpl.java:344)
23:46:40,809 ERROR [STDERR] 	at  
org.apache.openjpa.jdbc.sql.SelectImpl.execute(SelectImpl.java:318)
23:46:40,809 ERROR [STDERR] 	at  
org 
.apache 
.openjpa 
.jdbc 
.kernel 
.SelectResultObjectProvider.open(SelectResultObjectProvider.java:94)
23:46:40,809 ERROR [STDERR] 	at  
org.apache.openjpa.lib.rop.EagerResultList.<init>(EagerResultList.java: 
34)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.kernel.QueryImpl.toResult(QueryImpl.java:1223)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.kernel.QueryImpl.execute(QueryImpl.java:990)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.kernel.QueryImpl.execute(QueryImpl.java:842)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.kernel.QueryImpl.execute(QueryImpl.java:773)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.kernel.DelegatingQuery.execute(DelegatingQuery.java: 
525)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.persistence.QueryImpl.execute(QueryImpl.java:237)
23:46:40,810 ERROR [STDERR] 	at  
org.apache.openjpa.persistence.QueryImpl.getResultList(QueryImpl.java: 
277)

which is due to the missing implementation of the  
org.apache.openjpa.jdbc.sql.DBDictionary.toNativeJoin(Join join)  
method. Here is it taken from the OpenJAP 1.0.2 sources:

    /**
     * Use the given join instance to create SQL joining its tables in
     * the database's native syntax. Throws an exception by default.
     */
    public SQLBuffer toNativeJoin(Join join) {
        throw new UnsupportedException();
    }

After having discovered this I have changed my JoinSyntax setting from  
"database" to "sql92" and everything went fine.
Could anyone please explain me why?

Note: I'm using OpenJPA 1.0.2 along with MySQL 5.0.51a.

Any help is appreciated.

Best regards,
Francesco