Select random row from a PostgreSQL table with weighted row probabilities

Question

Example input:

SELECT * FROM test;
 id | percent   
----+----------
  1 | 50 
  2 | 35   
  3 | 15   
(3 rows)

How would you write such query, that

Answer 1

Here is something for you to play with:

select t1.id as id1
  , case when t2.id is null then 0 else t2.id end as id2
  , t1.percent as percent1
  , case when t2.percent is null then 0 else t2.percent end as percent2 
from "Test1" t1 
  left outer join "Test1" t2 on t1.id = t2.id + 1
where random() * 100 between t1.percent and 
  case when t2.percent is null then 0 else t2.percent end;

Essentially perform a left outer join so that you have two columns to apply a between clause.

Note that it will only work if you get your table ordered in the right way.