id is an integer ...
describe persons;
+------------+---------------------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra
|
+------------+---------------------------+------+-----+---------+-------+
| ID | int(11) | YES | | NULL |
I got a 0 count ...
SELECT COUNT(*) FROM persons WHERE ROUND(id) != id;
+----------+
| COUNT(*) |
+----------+
| 0 |
+----------+
1 row in set (0.06 sec)
On Mon, 2007-04-30 at 10:45 -0400, Jerry Schwartz wrote:
> Is your ID field an integer? If not, you might be running into some rounding
> corner cases. I don't see why that would happen, off-hand, since integers
> can be stored exactly as binary floating point numbers, but who knows.
>
> To satisfy your curiosity, you could
>
> SELECT COUNT(*) FROM table WHERE ROUND(id) != id;
>
> If you get a non-zero count, then you know that there is a possibility of
> CEIL(RND()) not hitting an ID.
>
> Regards,
>
> Jerry Schwartz
> Global Information Incorporated
> 195 Farmington Ave.
> Farmington, CT 06032
>
> 860.674.8796 / FAX: 860.674.8341
>
>
> > -----Original Message-----
> > From: John Kebbel [mailto:kebbelj@stripped]
> > Sent: Sunday, April 29, 2007 11:49 AM
> > To: MySQL
> > Subject: Re: Research Subjects drawn randomly from databases
> >
> > I rewrote my line using your suggestion ...
> >
> > select id,first,middle,last from persons order by rand() limit 10;
> >
> > and it worked perfectly. I'm still curious about why my
> > original version
> > gave such cockeyed results, but I'll focus on the successful solution
> > and leave that unsolved problem for another day. Thank you for your
> > solution Michael.
> >
> > On Sun, 2007-04-29 at 08:48 -0400, Michael Dykman wrote:
> > > If might suggest:
> > >
> > > SELECT * FROM BAR
> > > ORDER BY RAND()
> > > LIMIT 10
> > >
> > > On 4/29/07, John Kebbel <kebbelj@stripped> wrote:
> > > > For possible educational research purposes, I was playing
> > around with a
> > > > query that would randomly select people from a database.
> > The database I
> > > > experiment with has a group of fictitious persons with id numbers
> > > > (primary key) ranging sequentially from 2 to 378. When I ran these
> > > > queries below, I was expecting to select five random
> > persons from the
> > > > database. The query partially worked. I was getting
> > random subjects, but
> > > > everytime I ran the query, I got a different number of subjects,
> > > > stretching from 0 and up (sometimes as many as 8 or 9). I
> > could see the
> > > > query generating fewer rows if I duplicated an id or made
> > an off-by-one
> > > > error, but I don't see how it could generate more than
> > five. Does anyone
> > > > see my error? (I've used two equivalent forms for the
> > query below; both
> > > > did the same thing)
> > > >
> > > > select id,first,middle,last from persons where id =
> > ceil(rand()*377+1)
> > > > or id = ceil(rand()*377+1) or id = ceil(rand()*377+1) or id =
> > > > ceil(rand()*377+1) or id = ceil(rand()*377+1);
> > > >
> > > > select id,first,middle,last from persons where id in
> > (ceil(rand()*377
> > > > +1), ceil(rand()*377+1), ceil(rand()*377+1), ceil(rand()*377+1),
> > > > ceil(rand()*377+1));
> > > > +------+-------------+--------+----------+
> > > > | id | first | middle | last |
> > > > +------+-------------+--------+----------+
> > > > | 35 | Viridiana | W | McCarthy |
> > > > | 47 | Crystal | O | Cassady |
> > > > | 67 | Ricardo | L | Johnson |
> > > > | 183 | Christopher | E | Denver |
> > > > | 237 | Christopher | B | Brenner |
> > > > | 255 | Danielle | W | Nickels |
> > > > | 299 | Christine | D | Dexter |
> > > > | 300 | Rachel | J | Baker |
> > > > | 339 | Jenna | O | Murray |
> > > > +------+-------------+--------+----------+
> > > > 9 rows in set (0.00 sec)
> > > >
> > > >
> > > >
> > > > --
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> > > >
> > >
> > >
> >
> >
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