How does one generate random integers; first 5 values occur 2 times more than later values

Question

for the following code, how can I get the first 5 values to occur twice as often as the last 5 values?
Do I have to use nested loops?
Begin
  For n in 1 .. 10
  Loop
     dbms_output.put_line (ROUND(dbms_random.value(1, 10)));
End Loop;
End;

Answer 1

Hi,
If you had a lottery with 10 people participating, and you wanted to fix it so that each person had an equal chance of winning, what could you do?  One thing you could do is give tickets numbered 1, 2, 3, ..., 10 to the people, and then pick an integer in the range 1-10 at random.
If you had a lottery with 10 people participating, and you wanted to fix it so that 5 of the people were twice as likely to win as the other 5, what could you do?  One thing you could do is to give 2 tickets to the first 5 people, but only 1 ticket to the other 5.  Since you have 15 tickets now, you'd pick a random integer in the range 1-15.
Here's one way to do that in SQL.  The query below conducts 15 thousand lotteries.  We want the numbers 1-5 to get picked about 2000 times each, and the numbers 6-10 to occur about 1000 times each:
WITH got_n AS
    SELECT  MOD ( TRUNC (dbms_random.value (0, 15))
                , 10
                ) + 1    AS n
    FROM    dual
    CONNECT BY LEVEL <= 15000
SELECT    n
,         COUNT (*)    AS cnt
FROM      got_n
GROUP BY  n
ORDER BY  n
Sample output:
         N        CNT
         1       2048
         2       1939
         3       2020
         4       2066
         5       2007
         6        998
         7        967
         8       1004
         9        980
        10        971