#10060: Multiple table annotation failure
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Reporter: [email protected] | Owner:
Status: new | Milestone:
Component: ORM aggregation | Version: SVN
Resolution: | Keywords:
Stage: Accepted | Has_patch: 0
Needs_docs: 0 | Needs_tests: 0
Needs_better_patch: 0 |
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Comment (by bendavis78):
Regarding the example sql queries in comment 9
[http://code.djangoproject.com/ticket/10060#comment:9 above], I've
discovered that the first query is actually faster. My database has grown
fairly large in the past few months, so I've been able to test with more
clear results (this is using MySQL, by the way).
Using the JOIN method (where the aggregates are done in a derived join),
the query was extremely slow. It took over 30 minutes to execute with
57,000 rows in the users table. When I changed the query to the SELECT
method (where the aggregates are done in a subquery in the select clause),
the query took only 2 seconds with the exact same results. I spent a
whole day on this, and couldn't find a solid explanation for why the
derived join method was taking so long. I'd say at this point if anyone
moves forward with fixing this bug we should put the aggregate in the
subquery of the select clause.
I've looked around for an official stance on how to write a query with
multiple aggregations across different joined tables, and haven't come up
with a solid answer. If anyone does find "the right way" to do it, I'd be
interested to know -- I think that definitely needs to be settled before
this bug can be fixed.
--
Ticket URL: <http://code.djangoproject.com/ticket/10060#comment:16>
Django <http://code.djangoproject.com/>
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