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
--
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