Re: [hibernate-dev] Question regarding DISTINCT
The in-memory distincting is actually a temporary solution. There are a few JIRA cases making up the ultimate solution. But specifically to your questions, the DISTINCT applied to the query is intended to limit the data transferred by the JDBC driver from server to client, especially on large result sets or across poor networks. No, this is not controllable aside from using a custom query translator. Michael Barker wrote: Hi, When querying for a list of objects using ejb-ql, the keyword 'distinct' is used to de-duplicate the result set and give a correct list of objects. However I have noticed that everytime distinct is specifed in the ejb-ql query it also gets specified in the sql query. I am curious as the reasoning behind this. I understand that distinct is used to remove duplicates from the SQL result set, but from what I can see, for the majority of simple use cases the sql distinct is superflous. Running the hibernate generated query without the distinct returns the same results. I assume that the distinct is in there for are reason, are there some more complicated use cases for which the distinct in necessary? My main concern is performance, is there anyway of performing an ejb-ql select distinct... without hibernate issuing an sql select distinct Regards, Michael Barker. ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
Re: [hibernate-dev] Question regarding DISTINCT
Thanks Steve, Could you point me to the JIRA tasks, I would be interesting in seeing what the ultimate solution looks like? The thing that confuses me is that distinct generally doesn't come for free (generally resuls in a sort by the DB). If the result set is going to be the same anyway, isn't there an advantage to excluding the distinct clause, or is it simply not possible to determine which queries will benefit from it and which won't? Regards, Michael Barker. Steve Ebersole wrote: The in-memory distincting is actually a temporary solution. There are a few JIRA cases making up the ultimate solution. But specifically to your questions, the DISTINCT applied to the query is intended to limit the data transferred by the JDBC driver from server to client, especially on large result sets or across poor networks. No, this is not controllable aside from using a custom query translator. Michael Barker wrote: Hi, When querying for a list of objects using ejb-ql, the keyword 'distinct' is used to de-duplicate the result set and give a correct list of objects. However I have noticed that everytime distinct is specifed in the ejb-ql query it also gets specified in the sql query. I am curious as the reasoning behind this. I understand that distinct is used to remove duplicates from the SQL result set, but from what I can see, for the majority of simple use cases the sql distinct is superflous. Running the hibernate generated query without the distinct returns the same results. I assume that the distinct is in there for are reason, are there some more complicated use cases for which the distinct in necessary? My main concern is performance, is there anyway of performing an ejb-ql select distinct... without hibernate issuing an sql select distinct Regards, Michael Barker. ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
Re: [hibernate-dev] Question regarding DISTINCT
On Feb 19, 2007, at 3:32 PM, Michael Barker wrote: However I have noticed that everytime distinct is specifed in the ejb-ql query it also gets specified in the sql query. I am curious as the reasoning behind this. You are wondering why a DISTINCT you put into your query is actually send to the database in the generated SQL? ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
Re: [hibernate-dev] Question regarding DISTINCT
JIRA is searchable. Look for things marked as 'query-hql' as the component... The basic idea is to drop the collection-valued fetches. Is this where you will fetch collections in a sub-select rather than a join? Regards, Michael Barker. ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
Re: [hibernate-dev] Question regarding DISTINCT
You are wondering why a DISTINCT you put into your query is actually send to the database in the generated SQL? Yes, or more specifically, why DISTINCT is sent to the database in cases where result set will be the same with or without the DISTINCT clause. ___ hibernate-dev mailing list hibernate-dev@lists.jboss.org https://lists.jboss.org/mailman/listinfo/hibernate-dev
