[hibernate-dev] Question regarding DISTINCT

[Michael Barker]

Hi,

There is a small patch in JIRA (HHH-2440) that allows the user to 
specify that the generated SQL should not contain the distinct keyword.

Mike.

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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