Ignoring the limit problem for just a moment, what are the performance
characteristics? Does this form have a less steep rows vs. time curve?
As for the limit problem, that sounds a bit like a bug in MySQL and should
be addressed as such.
-JF
-Original Message-
From: MySQL List [mailto:[EMAIL PROTECTED]]
Sent: Thursday, June 27, 2002 2:44 PM
To: Jon Frisby
Cc: mysql
Subject: Re: Rand slowness.
I tried this, but it seems to be ignoring the LIMIT 3, since it
is returning
all the rows.
Try:
SELECT RAND() AS r, * FROM table ORDER BY r LIMIT 3;
Off the top of my head, I'd guess that the reason for the
slowdown has to
do
with MySQL doing a new RAND() call for every comparison in the sort
operation -- it wont stop sorting until it happens to get values back in
the
comparisons indicating that it has a correct ordering. The
odds of this
happening in a timely fashion *decrease* quite quickly as the number of
comparisons increases.
Selecting a random value *PER ROW* ensures that a comparison between any
two
given rows will always have the same result the second time you
try it as
it
did the first time you try it and will thus ensure deterministic and
reasonable sorting behavior.
-JF
-Original Message-
From: MySQL List [mailto:[EMAIL PROTECTED]]
Sent: Thursday, June 27, 2002 12:05 PM
To: mysql
Subject: Rand slowness.
Hi,
Is there a quicker way to get a selection of random rows than RAND()?
I basically use:
SELECT * FROM table ORDER BY RAND() LIMIT 3;
But I find that as the # of rows increases in table, it keeps
taking longer
and longer to get a result back. And I am talking a large increase,
basically 50 rows took about 1 second, 700 rows now takes almost a
minute.
I am not sure why the # of rows would affect RAND.
I am using the latest version of Mysql and php4 to get the rows.
-
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