Multiple rows returned trying to select specific row in Oracle SQL

Question

I am trying to return a value from field tid in a specific row in Oracle SQL but I am getting a weird behavior.

First, I tried this:

 select tid from
 (         


        

Answer 1

That is because dbms_random() is called for each row, so it can generate duplicate results. Instead, if you want one random row, try something like this:

select tid
from (select tid,
             row_number() over (order by dbms_random.value()) as seqnum
      from Train
     ) t
where seqnum = 1;

This will always return the row with "seqnum = 1", but it will be a random tid.