Tim Uckun, 21.10.2010 07:05:
No, it isn't. This is a three-way join between consolidated_urls, cu,
and tu --- the fact that cu is the same underlying table as
cu is an alias for consolidated_urls. tu is an alias for trending_urls.
There are only two tables in the query.
Yes, but consolidated_urls is there twice. Which makes it three relations
involved in the update
(consolidated_urls, cu and tu)
That's what Tom meant and that's where your cartesian product comes from.
select count(cu.id)
from consolidated_urls cu
inner join trending_urls tu on tu.consolidated_url_id = cu.id
That select is not the same as your UPDATE statement.
If your update statement was re-written to a plain SELECT it would be something
like
select count(consolidated_urls.id)
from consolidated_urls, consolidated_urls cu
inner join trending_urls tu on tu.consolidated_url_id = cu.id
See the difference?
Regards
Thomas
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