Originally Posted by Brujah

may need to use some code for it, like php or other
without knowing the values of probability index column, the first that comes to mind that it might get done is:

create a temporary table
insert into the temp table an id for each probability index difference
- if it's 83, put it in 83 times
- next one is 41, insert the id 41 times

select id from temp table order by rand();
select * from main table where temp table id = main table id;

maybe not elegant, but it's the first thing that came to mind without knowing if a mysql function exists to handle it easier