Biased random in SQL?

Question

I have some entries in my database, in my case Videos with a rating and popularity and other factors. Of all these factors I calculate a likelihood factor or more to say a b

Answer 1

I dare to suggest straightforward solution with two queries, using cumulative boost calculation.

First, select sum of boosts, and generate some number between 0 and boost sum:

select ceil(rand() * sum(boost)) from table;

This value should be stored as a variable, let's call it {random_number}

Then, select table rows, calculating cumulative sum of boosts, and find the first row, which has cumulative boost greater than {random number}:

SET @cumulative_boost=0;
SELECT
  id,
  @cumulative_boost:=(@cumulative_boost + boost) AS cumulative_boost,
FROM
  table
WHERE
  cumulative_boost >= {random_number}
ORDER BY id
LIMIT 1;