wangqi <wangqi(at)edgesoft(dot)cn> writes:
> SQL-3
> select * from wk_mclid1 where id1= (round((random() * (10-1))::integer)
> + 1)::integer;
> When we excute SQL-3,sometimes the result was 0 record or more than 1
> record.
> Why?
random() is re-evaluated for each row scanned by the SELECT.
If you don't want that, you can use a WITH to lock down the result of a
single random() call.
regards, tom lane