On Wed, Jun 13, 2001 at 03:25:55PM -0600, Matt Heaton wrote:
I can't seem to find a specificatoin on order by rand() and have a question.
Lets say a table has 10,000 rows in it, and I want to get one row that
matches
so I do a
select * from table where number=1 order by rand() limit 1;
What if 100 rows match? Does it first get all 100 rows and then randomly
choose one?
Ofcourse.
Or does it find the first one and stop? If it finds 100 rows and then
chooses one this
is VERY inefficient. If it finds one and then stops, what determines which
row it starts
searching on?
If it stops at the first one, it can't very well return a random one
from the set. It therefore has to find those 100 entries first.
If anyone knows FOR SURE how this works please let me know... I need to be
able to grab
a single row FAST even if a bunch of rows match. Let me know if you have
any ideas.
Let's just say the query is executed from left to right quite nicely.
With indexing on 'number' this should be quite fast, still.
Greetz, Peter
--
Against Free Sex! http://www.dataloss.nl/Megahard_en.html
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