[eluser]jedd[/eluser]
Your subject and your message conflict - do you mean another database, or another table?
For the code - DB random is apparently expensive, and so depending on how often you do this (it seems a silly thing to do, but, meh!) you may be better off doing a count(id), then using PHP's random function to identify an explicit row to get, and then get that row. Do some research / time tests.
Why are you using result_array() if you just want one row? Are you philosophically opposed to row_array() ?