[thesite] database: content table
rudy
r937 at interlog.com
Sat May 26 00:16:15 CDT 2001
> I was under the impression that subqueries were never
> the best way to go performance-wise. Is this not correct?
not as an absolute rule, no
in fact most subqueries (at least, the correlated kind) get parsed by the
optimizer into joins
some subqueries are indeed the fastest way to do something
for example
select contentname, datemod
from content
where datemod >=
(select max(datemod) from
from content
where userid=5)
this gets all the articles added after the last article added by djc
the subquery (inner query) is not related to the outer query -- it is not
correlated, i.e. its result is independent of the rows of the outer query,
consequently it can be retrieved first, the result stored in a variable,
and compared to datemod in each row of the outer table
rudy
More information about the thesite
mailing list