strange result for select * from table where id=random()*900 - Mailing list pgsql-sql

hi list,

this is my query:

select 
*
from _g2977 
where 
id=floor(random() * (900));

in table _g2977 i have id(s) from 1 up to 900. i just want to select one random dataset by the above query but i does
notwork.
 

actually i get sometime zero, sometimes one, sometimes two and sometimes even three results back from the above query
althoughi thought it should give only one random dataset from the table.
 

what is wrong?

i appreciate any help.

thanks in advance, stefan
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