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:[EMAIL PROTECTED] > 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 <[EMAIL PROTECTED]> 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) > > > > > > > > > > > > -- > > > MySQL General Mailing List > > > For list archives: http://lists.mysql.com/mysql > > > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > > > > > > > > > > > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
