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.
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