Thread

1. Bug? Me or PostgreSQL.

   Christopher Sawtell <csawtell@xtra.co.nz> — 2001-02-19T04:45:03Z

   Greetings,
   
   How can this happen?
   
   chris=# select name from boys_names where 
   boys_names.number=(random()*225+1)::int4;
     name
   --------
    Fred
    Gunnar
    Manuel
    Rainer
   (4 rows)
   
   Here is the table declaration:
   
   create table boys_names (
           number                  serial primary key,
           name                    varchar(20)
           ); 
   
   the details of my installation:-
   
   chris=# select version();
                                   version
   ------------------------------------------------------------------------
    PostgreSQL 7.1beta3 on i586-pc-linux-gnu, compiled by GCC egcs-2.91.66
   (1 row)
   
   -- 
   Sincerely etc.,
   
    NAME       Christopher Sawtell
    CELL PHONE 021 257 4451
    ICQ UIN    45863470
    EMAIL      csawtell @ xtra . co . nz
    CNOTES     ftp://ftp.funet.fi/pub/languages/C/tutorials/sawtell_C.tar.gz
   
    -->> Please refrain from using HTML or WORD attachments in e-mails to me 
   <<--
   
   
   

2. Re: Bug? Me or PostgreSQL.

   Tom Lane <tgl@sss.pgh.pa.us> — 2001-02-19T05:37:01Z

   Christopher Sawtell <csawtell@xtra.co.nz> writes:
   > How can this happen?
   
   > chris=# select name from boys_names where 
   > boys_names.number=(random()*225+1)::int4;
   >   name
   > --------
   >  Fred
   >  Gunnar
   >  Manuel
   >  Rainer
   > (4 rows)
   
   Er, what's your complaint exactly?  It's not obvious to me that
   there's anything wrong here.  You seem to have gotten random
   matches on four rows --- if that's ridiculously too low (or too
   high) you'd better explain why you think so.
   
   			regards, tom lane
   
   

3. Re: Bug? Me or PostgreSQL.

   Tod McQuillin <devin@spamcop.net> — 2001-02-19T05:47:14Z

   On Mon, 19 Feb 2001, Christopher Sawtell wrote:
   
   > How can this happen?
   >
   > chris=# select name from boys_names where
   > boys_names.number=(random()*225+1)::int4;
   >   name
   > --------
   >  Fred
   >  Gunnar
   >  Manuel
   >  Rainer
   > (4 rows)
   
   It's not clear what you expected to see -- I'll guess you expected only
   one row returned.
   
   But random() is being called once for every row in the table -- it's not
   surprising (if you have a lot of rows) that it comes up with a match more
   than once.  Sometimes it might even return no rows at all.
   
   SQL is not the best language for picking random members of a set.  You're
   better off picking a random number in a procedural language and passing
   that number as a constant to an embedded SQL query.
   -- 
   Tod McQuillin